氢冷发电机气体置换有几种方法？
参考答案：
氢冷发电机气体置换有两种方法，即抽真空置换法和中间介质置换法。
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—_____I could finish writing the report.[ ]
A.When it was that
B.It was when that
C.It was when
D.When was it that
2.
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4.
5.