that she discovered the double helix.
A) The scientist knew for a long time beyond a shadow of a doubt
B) For a long time, the scientist had known beyond a shadow of a doubt
C) For a long time, the scientist had known with great certainty
D) For a long time, the scientist knew beyond a shadow of a doubt
E) The scientist had known for a long time beyond a shadow of a doubt
问题：答案选C，理由是“beyond a shadow of a doubt”是俚语，这点我认同，但我对
C中用过去完成时很疑惑，觉得应该是"the scientist knew with great certainty that she had discovered the double helix."作者: chnp 时间: 2002-12-11 09:19
因为句首是for a long time，所以肯定应该用完成时态。而选项里只有一种完成时态。只能选它了。
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