外啮合齿轮泵的齿形渐开线不采用（）．
A、工字齿
B、直齿
C、斜齿
D、人字齿
参考答案：A
半固体接种时，不正确的是（）
A.用接种针
B.平行于管壁垂直刺入
C.必须接触管底
D.沿原路返回
E.整个过程要求无菌操作
The Turners ______ cards when a stranger ______ at the door.[ ]
A. played; was knocking
B. were playing; knocked
C. play; knocks
D. are playing; knocked
