For many years animals for carrying food and other supplies from one area to another has

问题补充：

For many years, animals for carrying food and other supplies from one area to another has been a means of living in Xinjiang Autonomous Region .

A. trained

B. training

C. having trained

D. to have trained

答案：

A. trained

(答案→)B. training

C. having trained

D. to have trained

解析：考查动名词作主语。本题的主语是动名词短语training animals for carrying food and other supplies from one area to another.谓语动词用单数形式。故B正确。C项是完成式，表示已经完成的动作，与句意不符。