物联网中常提到的“M2M”概念不包括下面哪一项（）
A.人到人
B.人到机器
C.机器到人
D.机器到机器
参考答案：A
—Why didn't you leave school? It's already eight o'clock.
—Because I _______ my homework yet. [ ]
A. wasn't finishing
B. wouldn't finish
C. haven't finished
D. wasn't finished
锅炉水位自动调节系统一般采用三冲量自动调节系统，三冲量是指（）、（）、（）。其中主参数是（）。
