My sister is ----- thinner than mt mother A:more B:much C:ve

答案：选B.much
解析：这三个选项中,只有much可以修饰形容词的比较级,表示更...,..得多的意思
翻译：我妹妹比我妈妈瘦得多.
另外：可修饰比较级的词
1）a bit,a little,rather,much,far,by far,a lot,still,even等
2）还可以用表示倍数的词或度量名词作修饰语.
3）以上词(除by far)外,必须置于比较级形容词或副词的前面.
典型例题:
1） ---- Are you feeling ____?
---- Yes,I'm fine now.
A.any well B.any better C.quite good
D.quite better
答案：B.any 可修饰比较级,quite修饰原级,well的比较级为better.
2）The experiment was____ easier than we had expected.
A.more B.much more C.much
D.more much
答案：C.much可修饰比较级,因此B,C都说得通,但easier本身已是比较级,不需more,因此C为正确答案.
3）If there were no examinations,we should have ___ at school.
A.the happiest time B.a more happier time
C.much happiest time D.a much happier time
答案：D.
有不明白的请继续追问,