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问题 单项选择题

汞的来源主要见于被污染的水产品，也可污染经废水灌溉后的农作物。一般烹调方法不能直接除汞，在以下方法中，哪一种较有效？（）

A．蒸煮

B．晒干

C．冻干

D．弃汤

答案

参考答案：D

选择题

There was no sign _______ they had died from diseases such as bird flu - the main worry in such cases. Among the theories was _______ a truck had collided（碰撞）with the crowd.  

A．/; that

B．that; that

C．that; which

D．that; /
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问答题 简答题

对管道法兰有什么具体要求？
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