Unless ____A_____ to answer question,the

题目

Unless ____A_____ to answer question,the
Unless ____A_____ to answer question,the students were not supposed to talk in Professor Brown's class.
A.asked B.being asked C.asking D.having asked
为什么选A,什么时候用B

答案

这里用过去分词表示被动,强调学生们在被问到的时候才可以讲话.所以选择A.选B的话,是用现在分词表示条件,需要描述学生主动的动作.如：When asking the questions,the students were supposed to talk in Professor Br...