1. C. The search for Alternative Sources of Energy
⇒ Dẫn chứng: The search for alternative sources of energy has led in various directions
2. D. Artificial made fuels
⇒ synthetic fuels: nguyên liệu nhân tạo
3. D. electricity
⇒ Dẫn chứng: Many communities are burning garbage and other biological products to produce electricity.....Some experts expect utility companies to revive hydroelectric power derived from streams and rivers
4. B. their being money consuming
⇒ Dẫn chứng: Experimental work is being done to deprive synthetic fuels from coal, oil shale, and coal tars. But to date, that process has proven expensive. Other experiments are underway to harness power with giant windmills. Geothermal power, heat from the earth, is also being tested
5. C. hydroelectric power
⇒ Fifty years ago hydroelectric power provided one-third of the electricity used in the United States but today it only supplies only four percent → " it" thay cho "hydroelectric power "
6. A. hydroelectric power will be the main source of energy
⇒ Dẫn chứng: Fifty years ago hydroelectric power provided one-third of the electricity used in the United States but today it only supplies only four percent. The oceans are another potential source of energy
* Một số từ vựng khác
+ geothermal (adj): thuộc đia nhiệt
+ convert (v): chuyển đổi
+ potential (adj): tiềm năng
+ underway (adj): đang thực hiện
