【题目】The shopkeeper did not want to sell for he thought was not enough.
A.where
B.how
C.what
D.which

【答案】C
【解析】考查介词宾语从句。for是介词，后面是宾语从句，从句缺少引导词，缺少主语，he thought是插入语，故选C。what在这里其双重作用。