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问题 单项选择题

钛及钛合金管与其他金属管道采用法兰连接时使用的非金属垫片一般为橡胶垫或塑料垫，并应控制氯离子含量不得超过()。

A．30×10-6

B．40×10-6

C．50×10-6

D．60×10-6

答案

参考答案：C

选择题

_____ in the mountains for a week, the two students were finally saved by the local police.

A．Having lost

B．Lost

C．Being lost

D．Losing
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选择题

The version _______ to be closest to the author’s original now belongs to a national museum in Paris.

A．was thought

B．thought

C．is thought

D．thinking
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