题目内容

They told us that they _________ for more than two hours.

A. had been waiting
B. were waiting
C. have waited
D. has waited

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Did you do what l _________ you to do yesterday?

A. have told
B. had told
C. had been telling
D. tells

We were hurrying because we thought the bell _________ .

A. had already rang
B. has already rang
C. had already rung
D. rang

从混杂细菌标本中分离病原菌用( )

A. 革兰氏染色镜检
B. 平板划线培养法
C. 半固体穿刺接种
D. 用暗视野显微镜观察
E. 纯培养法

细菌的外毒素大多在下列哪期产生( )

A. 稳定期
B. 对数生长期
C. 衰退期
D. 迟缓期
E. 以上都不对