阅读理解：
Putting Plants to Work
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.
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.
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.
36. What does the writer say about plants concerning solar energy?
B Plants have been used to produce solar energy.
D Plants have been a source of solar energy.
A Because they want algae to produce sugars and starches.
C Because they want to turn plant sugars to a new form of energy.
38. According to the fifth paragraph, under what conditions are algae able to use solar energy to make hydrogen?
B When there is no oxygen in the air.
D When enough starch is stored.
A It is not possible to remove sulfate from the environment.
C It is not easy to make sugars instead of hydrogen.
40. What is NOT true of algae?
B They can be a very good fuel source.
D They can be used in many ways.