信号筛管的缝隙、直径与生产筛管基本相同，只是长度较短，一般为1～2m。
参考答案：对
初产妇活跃期超过多少小时为活跃期延长（）。
A.8h
B.6h
C.12h
D.4h
E.10h
He has to be _____ bed _____ nine o'clock.[ ]
A. at; at
B. to; by
C. in; by
D. by; at
