XIX. 

1.will cycle

2.will be used

3.will have

4.will learn

XV.

3.i think biogas is abundant and cheap for cooking and heating

XVI.(tớ ghi đoạn tiếp nha bỏ đầu lúc lm thì nối vào thôi)

1.will be used more effectively for the future

2.will be solved by using solar energy

3.will be replaced by another renewable sourse

4.will be used to travel form place to another place

VOTE cho mình nha:))))

1.Source of energy will be used more by us for our future
2.The problem of energy shortage will be solved by us by using solar energy

3.Coal will be replaced by them by another renewable source
4. Flying cars will be used by them to travel from place to another place