All over Europe, and in North America, there're lakes and forests which are dead or (1) and the (2) is thought to be acid rain. What is acid rain Mr. Justin Cook, a scientist, explains: "All fossil fuels, (矿物燃料)，that (3) oil, coal and gas, contain sulphur. When these are burnt, for example (4) motor vehicles, they form sulphuric acid (硫酸)This (5) UP into the air, and soon it falls back to (6) , into lakes and (7) trees in forests." This can cause many local problems. (8) a result, lakes become acidic, fish disappear and trees are killed. The pollution is carried great distances by the wind, so sulphuric acid (9) in Britain can travel as far as Scandinavia (斯堪的纳维亚). Czech is one of the countries with the most acid rains and large areas of (10) consist only (11) dead trees.Is there (12) that can be done about acid rain Mr. cook says: "The rain (13) of acid rain is (14) power stations to install filters that (15) the acid getting out into the air. Here in Britain, the only (16) that has been taken is that the chimneys are built (17) so that the pollution is more distributed." If the petrol used in motor vehicles (18) lead--free, then it Would be possible to filter exhaust fuses (废气) which are a (19) cause of pollution. But these filter mechanisms (机械装置)can not work (20) the leads is removed. 19（）

A. great
B. minute
C. major
D. minor