不能说明“声音传播需要介质”的实验是 [ ]
A.
B.
C.
D.
答案：D
— What is she ? — She is . [ ]
A. does, sit
B. does, sits
C. does, sitting
D. doing, sitting
[1n(2x+1)一1n2x]=（）。
A．1
B．
C．0
D．-1
[1n(2x+1)一1n2x]=（）。