Give the correct form of the word given to complete the sentences: . _______unfortunately (không may là) ________, fossil fuels are harmful to the environment. (fortunate)

1. Tidal energy is renewable, plentiful and clean. (plenty)
2. Wind will be used as an enviromental friendly sources of energy. (environment)
3. There are many ways will be used to solve the problem of pollution (N). (pollute)
4. Solar power can be used to heat or cool our houses. (hot)
5. _______unfortunately (không may là) ________, fossil fuels are harmful to the environment. (fortunate)
6. We should use them_____economical (tiết kiệm )____ and try to find out alternative sources of power. (economy)
7. Solar energy is___renewable (tái tạo)_________, plentiful and clean. (renew)   
8. I think that solar energy can be an______alternative (thay thế )_____ source of energy in the near future. (alter)
9. We should reduce the use of_____electricity______ at home. (electrical) 
10. It’s a clean source of energy. Sailboats couldn’t move without this____power____. (powerful)
11. Waves will be used as an _____environmental____friendly sources of energy (environment)