问题
选择题
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
答案：B
题目分析：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。
点评：动名词做主语指经常性，习惯性的行为。单个的动名词做主语的时候，谓语动词用单数。