You may know citrus peel can get stains to come off,but do you know___________? A)how does it work B)what does it work C)what it works 請幫忙解答?

A) does work----verb group relating / co-ordinating to another verb group----how does it work=a noun clause referring and following the verb "know"====correct
"can get stains to come off"-- explaining the special quality it has------correct.
B)what does it work----what happened?------adj----incorrect
C)what it works-----tell me what it works on-----pronoun---works on itself-----incorrect.

本句句型:S + Vt + O，所以do you know是問句引導，後需接名詞子句what it works 當受詞，假如要接疑問句可寫成do you know " what does it work "?亦可

You may know (可能知道) citrus peel(柑橘類果皮) can get stains to come off(可擦去污斑), but do you know(但是你是否知道)___________?
(A) how does it work: 文法不合 – 疑問句之助動詞(do)，只於第一個動詞(know)使用一次(do you know)，之後的動詞(work)不再使用助動詞 ==> 用一般結構(主詞+動詞 ==> how it works)，故(A)為文法不合
(B) what does it work: 同上，文法不合
(C) what it works: 唯一文法合之選項