Coal is black solid fossil fuel. It is usually very (6)_______ . Coal is made of 65% - 95% carbon. It also has hydrocarbons and some other compounds in it. It is (7)_______ from the remain of plants that lived millions of years ago.

Coal can be burned for energy or (8)_______ . About two-third of coalmined today is burned in power station to make (9)_______ . Burning it is not as common as it used to be, (10)_______ it causes much pollution.

Natural gasis a mixture. It (11)_______ mainly of hydrocarbons. The main component is methane. Natural gas is often found in the ground (12)_______ with petroleum.

Most natural gas is burned (13)_______ to produce energy. It burns with a clean flame. It causes (14)_______ pollution.

The main use of natural gasis to produce electricity. It is also used as (15)_______ for cars, cooking gas and to make fertilizers.

6.  difficult 

7. founded

8.hotter 

9.  powder 

10. therefore

11. depends 

12. toghether

13.straightly 

14.  few 

15. . food