Sandycoulddonothingbuttohisteacherthathewaswrong.A.admitB.admittedC.admittingD.toadmit为什么不选B?(已经修理过多次)buttheenginestillcouldn'twork.(repair)wasrepairedmanytimes答案分析上说,这里b

Question

Sandy could do nothing but______to his teacher that he was wrong.
A.admit B.admitted C.admitting D.to admit
为什么不选B?
___________(已经修理过多次)but the engine still couldn't work.(repair)
was repaired many times
答案分析上说,这里but前后应该保持时态一致,
我想知道为什么第一个句子的时态不保持一致?

Answer 1

do nothing but do sth 是一个固定结构,意思是“除了.外什么也不能做”,这个句型里的第一个do是个实义动词,当不定式放在介词but,except,besides,后时,如果这些介词前有实义动词do的各种形式,也就是do,does,did,done时,那么介词后的不定式就不能带了,否则要带.例如：
He does nothing but play all day.(这里的does是个实义动词)
At the news she didn't say anything but to cry.（这里的did不是实义动词,say才是实义动词,所以后边的动词不定式符号to不能省略）