问题描述：
by the time he leaves university,he ( )much work experience so long as he takes a part time job
by the time he leaves university,he ( will have gained )much work experience so long as he takes a part time job.
为何不用has gained
by the time he leaves university,he ( will have gained )much work experience so long as he takes a part time job.
为何不用has gained
问题解答：
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