I had wanted to help you last night but I couldn't spare any time, for I a position which I have to hand in this morning.
A. wrote
B. was writing
C. had written
D. have written
网友回答
A. wrote
(答案→)B. was writing
C. had written
D. have written
解析：B 考察动词时态。句义:昨天我本想去帮助你，但我实在抽不出时间，因为当时我正在写作文，作文今天早上必修上交。根据语境可知此处表示过去某一时刻或某一阶段正在进行或者发生的动作。故使用过去进行时。故B正确。