I had wanted to help you last night but I couldn’t spare any time．for I an essay that is due this morning．
A. wrote
B. had written
C. was writing
D. have written
网友回答
A. wrote
B. had written
(答案→)C. was writing
D. have written
解析：考查时态。句意：我昨晚曾想帮助你来着，但是我腾不出时间。因为我正在写一篇今天上午要交的论文。结合语境可知描述的是过去正在进行的动作，故用过去进行时态，选C。