钢中声速约为5900m/s,2.5MHz声波的波长约为()。
A.2.36mm
B.2.36cm
C.0.42mm
D.0.42cm
参考答案:A
He was __ twenty when he was gone.
A.hardly
B.scarecely
C.badly
D.almost
录囚制度始于( )
A.汉代
B.明朝
C.清代
D.宋代