Plant Gas

　　Scientists have been studying natural sources of methane for decades but hadn"t regarded plants as a producer, notes Frank Keppler, a geochemist at the Max Planck Institute for Nuclear Physics in Heldelberg, Germany¹. Now Keppler and his colleagues find that plants, from grasses to trees, may also be sources of the greenhouse gas. This is really surprising, because most scientists assumed that methane production requires an oxygen-free environment.
　　Previously, researchers had thought that it was impossible for plants to make significant amounts of the gas. They had assumed that microbes² need to be in environments without oxygen to produce methane. Methane is a greenhouse gas, like carbon dioxide. Gases such as methane and carbon dioxide trap heat in Earth"s atmosphere and contribute to global warming.
　　In its experiments, Keppler"s team used sealed chambers that contained the same concentration of oxygen that Earth"s atmosphere has. They measured the amounts of methane that were released by both living plants and dried plant material, such as fallen leaves.
　　With the dried plants, the researchers took measurement at temperatures ranging from 30 degrees Celsius to 70 degrees C. At 30 degrees C, they found, a gram of dried plant material released up to 3 nanograms of methane per hour. （One nanogram is a billionth of a gram.） With every 10-degree rise in temperature, the amount of methane released each hour roughly doubled.
　　Living plants growing at their normal temperatures released as much as 370 nanograms of methane per gram of plant tissue per hour. Methane emissions tripled when living and dead plant was exposed to sunlight.
　　Because there was plenty of oxygen available, it"s unlikely that the types of bacteria that normally make methane were involved. Experiments on plants that were grown in water rather than soil also resulted in methane emissions. That"s another strong sign that the gas came from the plants and not soil microbes.

　　The new finding is an "interesting observation," says Jennifer Y. King, a biogeochemist at the University of Minnesota in St. Paul³. Because some types of soil microbes consume methane, they may prevent plant-produced methane from reaching the atmosphere. Field tests will be needed to assess the plant"s influence, she notes. 

词汇：

methane / mi:θeɪn/ n.  甲烷，沼气

emission / ɪ"mɪʃn / n. 散发，发射
geochemist / dʒi:ɒ"kemɪst / n. 地球化学家

triple / "trɪpl / v. 增加三倍；adj. 三倍的
Celsius / ˈselsiəs / n. & adj.  摄氏的

bacteria / bæk"tɪərɪə / n. (bacteriund的复数) 细菌
microbe / mi:θeɪn/ n. 微生物

nanogram / "neɪnəgræm / n. 微克
biogeochemist / baɪədʒi:ɒ"kemɪstrɪ / n. 生物地球化学家

chamber / "tʃeɪmbə(r) / n. 室，房间；腔

注释：

1.the Max Planck Institute for Nuclear Physics in Heldelberg, Germany.：马克思·普朗克核物理研究所，位于德国海德堡。海德堡系德国西南部城市，在巴登-符腾堡州的内卡河畔。海德堡大学是德国历史最悠久的大学。
2.microbe 细菌，意义同bacterium，但microbe不用作专门术语。
3.St.Paul：圣保罗，美国明尼苏达州首府。

hich statement is true of the methane emissions of plants in the experiment?

A:The lower the temperature, the higher the amount of methane emissions. B:Living plants release less methane than dried plants at the same temperature. C:When exposed to sunlight, plants stop releasing methane. D:The higher the temperature, the greater the amount of methane emissions.

第二篇 Good Table Manners Manners play an important part in making a favorable impression at the dinner table.Here are some general rules: Napkin(餐巾)use The meal begins when the host unfolds his or her napkin.This is your signal to do the same,so place your napkin on your lap.Unfold it completely if it is a small napkin,or in half,lengthwise(纵向地),if it is a large dinner napkin. If you need to leave the table during the meal,place your napkin on your chair as a signal to your server that you will be returning.Once the meal is over,place your napkin neatly on the table to the right of your dinner plate.Do not refold it. Use a napkin only for your mouth.Never use it for your nose,face or forehead. Use of utensils(餐具) Start with the knife,fork or spoon furthest from your plate,and work your way in,using one utensil for each course. If soup is served,remember to spoon away from yoursefl.This helps stop the drips.Do not put the entire soup spoon in your mouth.Instead,fill a soup spoon about 75 per cent with soup,and sip(啜饮)it from the side noiselessly. After finishing dinner,place the knife and fork parallel to one another across the plate with the knife alade facing inward toward the plate. Using your fingers Here’s a list of finger foods:sandwiches,cookies,small fruits or berries with stems,French fries and potato chips,and hamburgers. Chew(咀嚼)with your mouth closed and don’t make noise;don’t talk with your mouth full. Bread must be broken with your hands.It is never cut with a knife. Don’t pick something out of your teeth.Instead,excuse yourself to the bathroom. If possible,try not to cough at the table. Do not put your elbows(肘)on the table.In France,it is essential to have both hands above the table at the same time. Do not put bones or anything else on the table.Things that are not eaten should be put on your plate. hich of the following shows good table manners?

A:Talking with your mouth full. B:Putting bones on your plate. C:Putting your elbows on the table. D:Chewing with your month open.