人工挖孔桩的最小直径不宜小于（）
A.500mm
B.600mm
C.700mm
D.800mm
参考答案：D
由0,1,2,3,…,9十个数字和一个虚数单位i,可以组成虚数的个数为( )
A．100
B．10
C．9
D．90
I was born _______ the morning _______ February 25th, 1997. [ ]
A. in; of
B. on; in
C. in; in
D. on; of
