The unknown pervades the universe. That which people can see, with the aid of various sorts of telescope, accounts for just 4% of the total mass. The rest, however, must exist. Without it, galaxies would not survive and the universe would not be gently expanding, as witnessed by astronomers. What exactly constitutes this dark matter and dark energy remains mysterious, but physicists have recently uncovered some more clues, about the former, at least.
One possible explanation for dark matter is a group of subatomic particles called neutrinos. Neutrinos are thought to be the most abundant particles in the universe. According to the Standard Model, the most successful description of particle physics to date, neutrinos come in three varieties, called "flavors". Again, according to the Standard Model, they are point-like, electrically neutral and massless. But in recent years, this view has been challenged, as physicists realized that neutrinos might have mass.
The first strong evidence came in 1998, when researchers at an experiment, based in Japan, showed that muon neutrinos produced by cosmic rays hitting the upper atmosphere had gone missing by the time they should have reached an underground detector. Its operators suspect that the missing muon neutrinos had changed flavor, becoming electron neutrinos or-more likely-tau neutrinos. Theo- ry suggests that this process, called oscillation, can happen only if neutrinos have mass.
Over the coming months and years, researchers hope to produce the most accurate measurements yet. The researchers created a beam of muon neutrinos first. On the other side of the target sat a particle detector that monitored the number of muon neutrinos leaving. The neutrinos then travelled 750km (450 miles) through the Earth to a detector in a former iron mine in Soudan, Minnesota. Researchers then were able to confirm that a significant number of muon neutrinos had disappeared-that is, they had changed flavor. While their mass is so small that neutrinos cannot be the sole constituent of dark matter, they have an advantage in that they are at least known to exist.
The same cannot be said for sure of another possible form of dark matter being studied by a group of physicists in Italy. If the result continues to withstand scrutiny, it would appear to be evidence for an exotic new sort of fundamental particle, known as an axion, which could also be a type of dark matter.
How should we understand the process of oscillation

A:Cosmic rays are used to produce muon neutrinos. B:Muon neutrinos went missing during experiments. C:Cosmic rays hit the upper atmosphere. D:One flavor of neutrinos is changed into another one.

The unknown pervades the universe. That which people can see, with the aid of various sorts of telescope, accounts for just 4% of the total mass. The rest, however, must exist. Without it, galaxies would not survive and the universe would not be gently expanding, as witnessed by astronomers. What exactly constitutes this dark matter and dark energy remains mysterious, but physicists have recently uncovered some more clues, about the former, at least.
One possible explanation for dark matter is a group of subatomic particles called neutrinos. Neutrinos are thought to be the most abundant particles in the universe. According to the Standard Model, the most successful description of particle physics to date, neutrinos come in three varieties, called "flavors". Again, according to the Standard Model, they are point-like, electrically neutral and massless. But in recent years, this view has been challenged, as physicists realized that neutrinos might have mass.
The first strong evidence came in 1998, when researchers at an experiment, based in Japan, showed that muon neutrinos produced by cosmic rays hitting the upper atmosphere had gone missing by the time they should have reached an underground detector. Its operators suspect that the missing muon neutrinos had changed flavor, becoming electron neutrinos or-more likely-tau neutrinos. Theo- ry suggests that this process, called oscillation, can happen only if neutrinos have mass.
Over the coming months and years, researchers hope to produce the most accurate measurements yet. The researchers created a beam of muon neutrinos first. On the other side of the target sat a particle detector that monitored the number of muon neutrinos leaving. The neutrinos then travelled 750km (450 miles) through the Earth to a detector in a former iron mine in Soudan, Minnesota. Researchers then were able to confirm that a significant number of muon neutrinos had disappeared-that is, they had changed flavor. While their mass is so small that neutrinos cannot be the sole constituent of dark matter, they have an advantage in that they are at least known to exist.
The same cannot be said for sure of another possible form of dark matter being studied by a group of physicists in Italy. If the result continues to withstand scrutiny, it would appear to be evidence for an exotic new sort of fundamental particle, known as an axion, which could also be a type of dark matter.

A:Cosmic rays are used to produce muon neutrinos B:Muon neutrinos went missing during experiments C:Cosmic rays hit the upper atmosphere D:One flavor of neutrinos is changed into another one

Passage Four
As he closed his service station at 1:20 one Sunday morning, Tony Payseur set on the ground a metal cash box containing $7000. At home a short while later, he reached in the back of his car for the box. It was missing.
Realizing that he must have left it outside the station, Payseur speeded back. The box was gone. Sunday morning; although he felt iii, Payseur went to work with his two sons. Then, in the middle of the afternoon, a man named Wayne came and told his story. Passing the station minutes after Payseur left the previous night, Brazzell had spotted the metal box. Thinking it was a tool-box someone had left accidentally, he stopped and picked it up. About 3 p. m. Sunday, Brazzell opened the box. Finding it filled with cash, he rushed to the station.
"I couldn’ t believe someone would be so honest," Payseur said it when he got back his box.

A:How the missing metal box was returned. B:Mr. Payseur is a lucky man. C:Mr. Payreur' s metal box. D:Mr. Payseur' s carelessness.

The missing man was found ______ in the back of the truck.

A:wrapped B:fixed C:fastened D:bound

Passage Four As he closed his service station at 1:20 one Sunday morning, Tony Payseur set on the ground a metal cash box containing $7000. At home a short while later, he reached in the back of his car for the box. It was missing. Realizing that he must have left it outside the station, Payseur speeded back. The box was gone. Sunday morning; although he felt iii, Payseur went to work with his two sons. Then, in the middle of the afternoon, a man named Wayne came and told his story. Passing the station minutes after Payseur left the previous night, Brazzell had spotted the metal box. Thinking it was a tool-box someone had left accidentally, he stopped and picked it up. About 3 p. m. Sunday, Brazzell opened the box. Finding it filled with cash, he rushed to the station. "I couldn’ t believe someone would be so honest," Payseur said it when he got back his box.

A:How the missing metal box was returned. B:Mr. Payseur is a lucky man. C:Mr. Payreur' s metal box. D:Mr. Payseur' s carelessness.

The missing bird ______ from the hole in the cage.

A:would be escaping B:must have escaped C:might as well escape D:was to have escaped

Where was it ______ she found her missing handbag

A:that B:where C:the place where D:in which