他已经绞尽脑汁了，可是仍未找出问题的答案。
He had racked his brain, but he still couldn't work out the answer to the problem.
绞尽脑汁to rack onesbrain他已经绞尽脑汁了，可是仍未找到问题的答案。
He had racked his brain, but hadn't been able to work out the answer to the problem.
绞尽脑汁to rack onesbrain他已经绞尽脑汁了，可是仍未找到问题的答案。
He had racked his brain, but hadn't been able to work out the answer to the problem.
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