【题目】Before the end of the nineties, air pollution ______ a serious problem that endangers the health of the human race. ( )
A.will be becomeB.will become
C.will have becomeD.will have been become
【答案】C
【解析】
句意：在90年代末之前，空气污染将成为一个严重的问题，那会危及人类的健康。根据句意，此句要用将来完成时，将来完成时的结构： shall/will have+过去分词。故选C。
