So difficult it to acquire a large vocabulary without the help of a teacher that he was cl

问题补充：

So difficult it to acquire a large vocabulary without the help of a teacher that he was close to giving up .

A. he have felt

B. have he felt

C. he did feel

D. did he feel

答案：

A. he have felt

B. have he felt

C. he did feel

(答案→)D. did he feel

解析：在so...that结构中，若将表示程度的状语“so+adj./adv.”置于句首，主句中需用倒装语序，从句中的时态决定着主句中须用一般过去时。