800score中的一题

redli

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."

chnp

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。