The doctor will not perform the operation ___ it is absolutely necessary.A．whenB

题型：不详难度：来源：

The doctor will not perform the operation ___ it is absolutely necessary.

A．when

B．if

C．for

D．unless

答案

解析

略

举一反三

Go back ___ you came from.

A．until

B．where

C．which

D．when

题型：不详难度：| 查看答案

He lay ___ the grass was the thickest.

A．where

B．when

C．that

D．after

题型：不详难度：| 查看答案

You will find friendly people ___ you go in China.

A．where

B．and

C．wherever

D．so

题型：不详难度：| 查看答案

___ it was already dark, they went on working in the fields.

A．If

B．Whether

C．But

D．Though

题型：不详难度：| 查看答案

___ he has finished writing the novel is unknown.

A．If

B．Whether

C．When

D．While

题型：不详难度：| 查看答案

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