Lydia really regrets ________ out of high school．She has really had to struggle to make a living because of that decision．

A.drop

B.to drop

C.dropping

D.dropped

答案及解析： C

解析：

考查非谓语动词。根据下一句可知Lydia“后悔”从高中辍学。regret to do sth表示“遗憾地去做某事”，不符合所给语境。