At one time we had about eighty people here who did nothing but ___ into his family

来源：百度知道 编辑：UC知道 时间：2024/05/01 21:59:49
At one time we had about eighty people here who did nothing but ___ into his family history.(D)
A.to research B.researched C.researching D.research

请详解一下，同时翻译一下

do ...but do
前面不是do而是其他动词的话就是 动词..but to 动词

以前我们大约有八十来个人不做其他事，只是调查他的家庭史

应该是not do but do的句式。
从前这80个人什么也没做，只是调查了他的家庭历史。
才疏学浅，仅供参考。