康德拉耶夫周期是—种()。
A.短周期
B.中周期
C.长周期
D.不能确定
参考答案：C
It's seven o'clock. He may__________.
A. go to the school
B. go to school
C. goes to school
D. goes to the school
采集固定源污染源排气中丙烯腈所用的活性炭粒度为（）目
A.20～40
B.40～60
C.60～80
D.80～100
