问题描述：
The doctor has done everything he can _____ (save)the patient.
It 's a waste of time to spend so much time on computer games.(保持句意不变）
It isn't _____ ____ so much time on computer games.
It 's a waste of time to spend so much time on computer games.(保持句意不变）
It isn't _____ ____ so much time on computer games.
问题解答：
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