题目内容：

i am trying to find a knife ___this pencil A which to sharp with B to sharpen选哪个

优质解答

选B to sharpen
which 是用在定语从句的引导词,楼主的句子后面只跟了一个名词this pencil,不需要从句,如果一定要用which,可以说：I am trying to find a knife which sharpens this pencil.