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【单选题】
属于中枢神经系统抑制剂的是A.
酒精
B.
可卡因
C.
海洛因
D.
丙酮
E.
仙人掌毒素
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皮皮学刷刷变学霸
举一反三
【多选题】在液压传动中，液压油既是液压传动系统实现能量转换、传递和控制的工作介质，又有一般润滑油在机械中所起的（）等作用。
A.
润滑
B.
冷却
C.
防锈
D.
减震
E.
磨损
【单选题】Although chatting on line has exploded in popularity in recent years, there is no ________ for a face-to-face conversation.
A.
privilege
B.
affection
C.
substitute
D.
adjustment
【单选题】The primary line module has failed and the spare line module is nowactive.What occurs，by default，when the primary line module returns to an operational status？（）
A.
The primary line module is inactive for five minutes and then becomes active.
B.
The primary line module is in standby mode，while the spare line module remains active.
C.
The primary line module becomes active immediately and the spare line module becomes inactive.
D.
The primary and spare line modules are active for five minutes，after which time the spare line module becomes inactive.
【简答题】The firm has decided to switch to another line of products, as these __________(不畅销).
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