【题目】It may be necessary to stop______in the learning process and go back to the difficult points in the lessons.
A. at intervals B. at random
C. at ease D. at length
在线课程【答案】A
【解析】A 考查介词短语辨析。A．at intervals 不时；B．at random随意的；C．at ease自在的；D．at length详尽地；句意：可能有必要学一定的内容再停下来回顾一下本课的难点。根据语境可知选A项。