8. We will cut down in the use of natural gas because it is …….. and harmful to the environment. A. available B. abundant C. plenty D. limited 9. …………….. source of energy is the source that can’t be replaced after use. A. Effective B. Non-renewable C. Renewable D. Natural 10. Which of the following is NOT renewable source of energy? A. wind B. coal C. hydro D. solar 11. We are looking for cheap, clean and……………sources of energy. A. serious B. dangerous C. effective D. efficient 12. If we go on…………….electricity, we will have to pay a lot next month. A. turning on B. widened C. wasting D. increasing 13. Biogas is …………….and cheap for cooking and heating. A. serious B. expensive C. plenty D. abundan