Only in recent years have people become aware of the importance of environmental protection and ________ various measures to prevent pollution from becoming progressively worse.
(A)began to take
(B)they begin to take
(C)begun to take
(D)do they begin to take
標準答案為C。動詞不是為become aware of 為現在式嗎?
考的是平行結構的問題,我選擇A,但我看不知道為啥要選擇C呢。請高手幫忙巴。