练习：
1. 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.
2. Why 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.
3. 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.
4. 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.
5. 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.
6. Why 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 starch.
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.
