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【单选题】
下面几种叙述中,哪一种是正确的?( )A.
双头螺柱是因为两头有螺纹，在装配时两头可以任意选装；
B.
双头螺柱的使用场合与螺钉和螺栓一样；
C.
双头螺柱使用于零件的被连接部位太厚（不能钻通孔）而另一个零件又经常需要拆卸的场合；
D.
双头螺柱因为有两个头，装配时才不必配上垫圈。
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皮皮学刷刷变学霸
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【简答题】波长为( )—( )μm的部分称为热红外线。我们周围的物体只有当它们的温度高达( )°C以上时,才能够发出可见光。相比之下,我们周围所有温度在绝对零度(-273°C)以上的物体,都会不停地发出热红外线。
【单选题】On a cargo ship, fire and boat drills are carried out _____.
A.
once a week
B.
once a month
C.
once a year
【简答题】Once upon a time there were two good friends. One is a captain of a ship ,the other is a merchant (商人). The merchant had a young son，who wanted to be a sailor ，so the captain took him for voyages(航海) ...
【单选题】The Ship Security Alert System is checked once a month
A.
The SSAS is checked two times a month
B.
The SSAS is checked one time a month
C.
The SSAS is checked once a week
D.
The SSAS is checked every week
【单选题】Once a ship, you don't need to worry about meals or entertainment.
A.
on occasion
B.
on board
C.
in position
D.
in operation
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