The knife -----we used to cut the bread is very sharp. A which B with C with which

why

C

C 用刀是 with the knife要介词

C把它代入可以这样We used to cut the bread with the knife~~which在句子中作with的宾语

C

cut with  the  knife用刀切，which引导的定语从句

选C

这个句子的意思是：我们用来割东西的那把小刀很锋利。   cut A with B：用B来切割A。   the knife 是主语，   with which we used to cut things是定语从句，其中which不能改成that，因为在定语从句中，介词后面的关系代词只能用which。   is是系动词   very是副词，用来修饰形容词sharp，   sharp是形容词做表语。

C.The knife with which we used to cut the bread is very sharp.

我们用来切面包的刀很锋利。