英语单选Mostofusknowweshouldcutdownonfat,butknowingsuchthingsisn'tmuchhelpwhenitshoppingandeating.A.referstoB.speaksofC.focusonD.comestoFirst,句中","后为什么用knowing,而不用know.Second,正确答案是什

Question

英语单选
Most of us know we should cut down on fat,but knowing such things isn't much help when it_____shopping and eating.
A.refers to B.speaks of C.focus on D.comes to
First,句中","后为什么用knowing,而不用know.Second,正确答案是什么.望简洁易懂的答案,并把句子翻译一下,望翻译得流畅准确一些.

Answer 1

选D.comes to
我们多数人都知道要减肥,但知道这些事并不能起多大作用,特别是当我们谈到购物和饮食的时候.
when it comes to 是固定说法,意思是：
1.一谈到……；就……而论
2.当谈论到…,涉及到
3.当提到
knowing such things 是主语,动词要做主语有两种变法：一是加ing变成动名词,一是加to变成不定式.所以这里不能用know.