下列各项中，能证明基因与染色体具有平行关系的实验是[ ] A．摩尔根的果蝇杂交实

My teacher _____ me the key to the classroom but I’m afraid I _____ it.

A．had given, lost

B．has given, lost

C．gave, have lost

D．has given, have lost

He ___ the heavy rain when he was on the way to school.

A．had caught in

B．was catching

C．caught by

D．got caught in

如图所示的电位器实质是一种______，它是靠改变连入电路的电阻线的______来改变电阻值的．

汽旋塞被填料堵死造成玻璃管内水位高于实际水位故障时，应（）

A、更换汽旋塞

B、冲洗水旋塞

C、加强排污

D、冲洗汽旋塞

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