微量元素 microelement, trace element

微量元素(trace element, microelement)

微量元素（trace element或microelement）

trace命令提供（）到（）的每一跳的信息.

Memory is the ability to keep track of things that have happened in the past. Memory really is learning. One needs memory to ride a bicycle. A dog needs to remember if it is to come when called.
Memory is said to be stored in the brain as a "memory trace (记忆痕) ". What makes up this trace is not known. Some scientists believe that certain chemical substances may carry certain memories. For example, one substance, when given to rats, causes them to fear the dark.
Other research into memory has to do with how the brain works. Psychologists use three means to find out bow a person remembers. For example, give a person a grocery list. Let the person memorize the list, then put it away. The most natural way to find out how much a person remembers of the grocery list is to ask what he or she remembers. This is called the method of recall. Another method is called recognition. Give the person another grocery list. Ask him or her to choose items on the first list from the items that are on only the second list. Often a person will be able to recognize things that he or she cannot recall. A third method of finding how much a person remembers is called relearning. Here the person is asked to read over the first list. The person will probably learn the list the second time faster than he did the first time. The difference in the time it takes to relearn the list is thought of as measure of how much a person has remembered.
One way of remembering something is to repeat it many times. Interest is very important. Boring lists of facts are much more difficult to remember than something that we understand and are interested in. Motivation, or wanting to do something, is also important. Motivation is linked with reward. For example, a hungry animal quickly learns how to do something if that action gets the animal food. In humans, wanting to learn is often motivation. The praise of a teacher or the knowledge that an answer is correct is rewarding.

We can learn from the 2nd paragraph that （）

A:bad memories may cause rats to fear the dark B:it is hard to tell what a memory trace consists of C:chemical substances carry certain memories D:memory is stored in the brain as a substance

The Bermuda Triangle is one of the greatest mysteries of the sea. In this triangle area between Florida, Puerto Rico and Bermuda in Atlantic, ships and airplanes seem to disappear more of ten than in other pans of the ocean. And they do so without leaving any sign of all accident or any dead bodies.
It is said that Christopher Columbus was the first person to record strange happenings in the area. His compass stopped working, a flame came down from the sky, and a wave 100 to 200 feet high carried his ship about a mile away.
The most famous disappearance in the Bermuda Triangle was the U. S. Naval Air Flight 19. On December 5, 1945, five bomber planes carrying 14 men took offon a training mission from the Florida coast. Later that day, all communications with Flight 19 were lost. They just disappeared without a trace.
The next morning, 242 planes and 19 ships took part in the largest air-sea search in history. But they found nothing.
Some people blame the disappearances on supernatural forces. It is suggested the missing ships and planes were either transported to other times and places, kidnapped by aliens or attacked by sea creatures.
There are also natural explanations, though. The U. S. Navy says that the Bermuda triangle is one of two places on earth where a magnetic compass points towards true north instead of magnetic north. Therefore, planes and ships can lose their way if they don’t make adjustments.
The area also has changing weather and is known for its high waves. Storms can turn up suddenly and destroy a plane or ship. Fast currents could then sweep away any trace of an accident.
Why the Bermuda Triangle is regarded as one of the greatest mysteries of the sea according to the passage

A:Because many ships have turned over in this area. B:Because many ships and planes have disappeared here without any trace. C:Because not only ships but also planes have disappeared in this area. D:Because nobody has ever been ther

Trace命令用于跟踪测试数据转发( )。

trace命令用于______。

A:查看配置文件 B:判断网络的连通情况 C:跟踪测试分组转发路径的每一步 D:查看系统时钟、Flash的使用情况