Is "the third arm“ = ”the third wheel "? "I don't want to be the third arm." What's the meaning of this sentence? Can the "third arm" be instead of by "third wheel"? Thank you.

how can i say "do this tap dance with you kids" in another way? Here is the sentence I read: i don't want to do this tap dance with you kids here. And now wondering, may I say in these forms: i don't want to play around here.( if it's wrong, what's the right way?) i don't want to do the play house here, .( if it's wrong, what's the right way?) Is there another way to say "do this tap dance with you kids..."? Thank you.

could the words "they're" here be replaced by "it's"? -If you don't want to get teased about that,get a doctorate. -I have one, they're great. why here is "they're" but not "it's"? Thank you.

"work for me" vs."work on me" Here is Sherclock S02E01 dialogue: Maid: Works for me. Irene Adler: Everything works on you What's the difference between these two: "work for me" and "work on me"? Could it be changed into: 1) - Works for me. - Everything works for you. or 2) - Works on me. - Everything works on you. ? Thank you.

“马蹄铁效应”的英文原句是怎么说的？ “马蹄铁效应”：断了一枚钉子，掉了一只蹄铁；掉了一只蹄铁，折了一匹战马；折了一匹战马，摔死了一位将军；摔死了一位将军，吃了一场败仗；吃了一场败仗，亡了一个国家……。 这个英文原句是怎么说的？谢谢！

"help sb. in doing sth." vs "help sb. to do sth." Is it correct to say "help sb. in doing sth."? If it's right, what's the difference with "help sb. to do sth." ? and,which one would be much oral? thx. :)

"the only thing i can do is love him"? OR "the only thing i can do is to love him"? which one would be the right one? OR both r right? Thz.

"might do sth." vs. "might be doing" vs. "might have done" Grammar, sometimes, is a mystery. My friends & I discussed one of it for a long time yesterday evening,but still have no idea. Here is it: What's the difference of next three: 1 might have an affair 2 might be having an affair 3 might have had an affair and, why, in BBC's Sherlock,there is "I think my husband might be having an affair. "? But not "I think my husband might have an affair." Thank you very much for any reply. thank you! But here still the question: Can we say "I think my husband might have an affair." instead of "I think my husband might be having an affair. "? They're the same?