12
(A)Many scientists believe that some cows’ nervous systems were stricken by a sheep disease called scrapie.
(B)These large doses accumulate in animal organs and are eaten by humans.
(C)Many people want to ban irradiated food because they are not sure such food is safe.
(D)The need to maintain a prosperous agricultural economy has led to many difficulties.

Cows do not eat meat in their natural surroundings, but farm industries in many countries began feeding cows the ground-up parts of dead sheep. 

(a)

Many scientists believe that some cows's  nervous systems were stricken by a sheep disease called scrapie. 

 According to them,

The struggle to save the food supply from damage did not end with Silent Spring. 

11 For example, in order to increase the protein蛋白質 in cattle牛, people began to alter the diet of cows.

Cows do not eat meat in their natural surroundings, but farm industries in many countries began feeding cows the ground-up parts of dead sheep. 

12 According to them, this harmful process, begun by humans for greater profits, led to outbreaks of “mad cow disease” in the United States.

(A)Many scientists believe that some cows’ nervous systems were stricken by a sheep disease called scrapie羊搔癢症. 

(B)These large doses accumulate in animal organs and are eaten by humans. 
(C)Many people want to ban（尤指官方）禁止 irradiated（用來治療或診斷用的）光（或其他輻射） food because they are not sure such food is safe. 

(D)The need to maintain繼續有, 維持；保持 a prosperous繁榮的；富裕的 agricultural農業 economy has led to many difficulties.