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问题 单项选择题

下图为植物组织培养的基本过程，则制作人工种子，及生产治疗烫伤、割伤的药物——紫草素，应分别选用编号是的（）

A．④② 

B．③② 

C．③④ 

D．④③

 

答案

参考答案：B

单项选择题

设计继电器—接触器式控制系统的主电路后，应设计满足各电动机运转功能和与工作状态相对应的（）

A、信号电路

B、控制电路

C、照明电路

D、执行电路
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单项选择题

Many students do not like tostudy history(历史)．They say that there are (41) many names and dates to (42) ．But if we do not know about the (43) ，we can not understand the present well．For example，if we wish to know how men (44) to use fire，we have to know what men did (45) the past to travel at night or to keep themselves (46) in cold nights．Only a study of history will make US realize(意识到) (47) everything we do today is the result of what (48) people did in the past．

[A] that [B] which [C] what

As we (49) history，we learn many interesting (50) ．History helps US understand our present life better．
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