产道是胎儿产出的必经之路，硬产道是指（）。
A.骨盆
B.子宫
C. * *
D. * * 前庭
E.脊柱
参考答案：A
I just don’t understand ________ that prevents so many children at school from being as happy as one
might expect.[ ]
A. what it is
B. what it does
C. what is it
D. why is it
显微镜法计数白细胞时，通常加外周血
A．40μl
B．30μl
C．20μl
D．10μl
E．50μl
