Sandy could do nothing but ____ to his teacher that he was wrong

Sandy could do nothing but ____ to his teacher that he was wrong.
A、admit
B、admitted
C、admitting
D、to admit
【正确答案】：A
【题目解析】：考查介词but 用法，but前的动词是do /does/did，but后的动词要用原形动词，所以选A。