每题3分，共45分）
下面有3篇短文，每篇短文后有5道题，每题后面有4个选项。请仔细阅读短文并根据短文回答其后面的问题，从4个选项中选择1个最佳答案涂在答题卡相应的位置上。
第一篇
Putting Plants to Work
Using the power of the sun is nothing new. People have had solar-powered calculators and buildings with solar panels for decades. But plants are the real experts： Theyve been using sunlight as an energy source for billions of years.
Cells in the green leaves of plants work like tiny factories to convert sunlight， carbon dioxide， and water into sugars and starches， stored energy that the plants can use. This conversion process is called photosynthesis. Unfortunately， unless youre a plant， its difficult and expensive to convert sunlight into storable energy. Thats why scientists are taking a closer look at exactly how plants do it.
Some scientists are trying to get plants， or biological cells that act like plants， to work as miniature photosynthetic power stations. For example， Maria Ghirardi of the National Renewable Energy Laboratory in Golden， Colo.， is working with green algae. Shes trying to trick them into producing hydrogen instead of sugars when they perform photosynthesis. Once the researchers can get the algae working efficiently， the hydrogen that they produce could be used to power fuel cells in cars or to generate electricity.
The algae are grown in narrow-necked glass bottles to produce hydrogen in the lab. During photosynthesis， plants normally make sugars or starches. “But under certain conditions， a lot of algae are able to use the sunlight energy not to store starch， but to make hydrogen.” Ghirardi says. For example， algae will produce hydrogen in an airfree environment. Its the oxygen in the air that prevents algae from making hydrogen most of the time. Working in an airfree environment， however， is difficult. Its not a practical way to produce cheap energy. But Ghirardi and her colleagues have discovered that by removing a chemical called sulfate from the environment that the algae grow in， they will make hydrogen instead of sugars， even when air is present.
Unfortunately， removing the sulfate also makes the algaes cells work very slowly， and not much hydrogen is produced. Still， the researchers see this as a first step in their goal to produce hydrogen efficiently from algae. With more work， they may be able to speed the cells activity and produce larger quantities of hydrogen.
The researchers hope that algae will one day be an easy-to-use fuel source. The organisms are cheap to get and to feed， Ghirardi says， and they can grow almost anywhere： “You can grow them in a reactor， in a pond. You can grow them in the ocean. Theres a lot of flexibility in how you can use these organisms. ”
31 What does the writer Say about plants concerning solar energy？_______
A Plants are the real experts in producing solar energy.
B Plants have been used to produce solar energy.
C Plants have been using solar energy for billions of years.
D Plants have been a source of solar energy.
32Why do some scientists study how plants convert sunlight carbon dioxide， and water into sugars and starches？ _______
A Because they want algae to produce sugars and starches.
B Because they want green plants to become a new source of energy.
C Because they want to turn plant sugars to a new form of energy.
D Because they want to make photosynthesis more efficient.
33 According to the fifth paragraph， under what conditions are algae able to use solar energy to make hydrogen？ _______
A When there is a lot of oxygen in the air.
B When there is no oxygen in the air.
C When photosynthesis is taking place.
D When enough starch is stored.
34 Researchers have met with difficulties when trying to make algae produce hydrogen efficiently. Which one of the following is one such difficulty？ _______
A It is not possible to remove sulfate from the environment.
B It is not possible to work in an airfree environment to produce hydrogen.
C It is not easy to make sugars instead of hydrogen.
D It is too slow for algae to produce hydrogen when the sulfate is removed.
35 What is NOT true of algae？ _______
A They are easy to grow.
B They can be a very good fuel source.
C They are cheap to eat.
D They can be used in many ways.