1."It's not at all polite!" VS "it's not polite at all!"
- both are correct, although here, the second one is more common
2."Welcome to the New York City Lost and Found Office." VS "Welcome to the Lost and Found Office in New York City."(both are right? Is there any difference between them?)
- the first one, as it is the name of the department. We don't use "in" unless we are comparing it with somewhere else, as "The Lost and Found Office in New York is better than the one in San Francisco"
3.is-isn't, do-don't, did-didn't, must-mustn't, shall-?
- "shall not" - there is no contraction involving shall
4."People from foreign countries have different body language from us." Why not use "body languages"?
- there is only one "body language"
5.When "any" in the negative sentences/interrogation questions, we should use the noun like this,dog,pen,book,but not dogs,pens,books,yes?
Like this...We don't have any pen.(right)
We don't have any pens.(wrong)
- this is not correct, with "any" you need to use plurals, "We don't have any pens" is right