volunteer用作不及物动词时，其后常跟介词for、in等。volunteer用作形容词的意思是自愿的、志愿的。常见的短语是volunteer for或者volunteer in。
例句She now helps in a local school as a volunteer three days a week。目前她在当地的一家学校做志愿工作，一周去3天。Right. What I want now is two volunteers to come down to the front。好了，现在我需要两个自告奋勇的人到前面来。
