Question

当时我怀疑我是否别无选择只能放弃了。

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Answer

I doubted whether I had no choice but to give it up at that time.

【解析】

根据汉语提示可知，句中时态为一般过去时；I我；doubt怀疑，其过去式为doubted；whether是否；I had no choice but to give it up我别无选择只能放弃；at that time在那时，当时；I是主语，doubted是谓语，宾语是由whether引导的宾语从句充当，从句部分语序为陈述语序。故填I doubted whether I had no choice but to give it up at that time.