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
网友回答
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。