Many high schools ask their students to spend a certain number of_英语解答

Many high schools ask their students to spend a certain number of hour _volunteering_ every day.
这是一道选正确形式填空,volunteering.但是我实在是看不懂为什么吖~

人气：404 ℃　时间：2019-10-24 13:01:55

解答

sb.spend + 时间+（in）doing sth.某人花费时间做某事,是固定搭配