I borrowed this fake example from the [other question][1] (in my revisions).

> I saw a girl dancing at a club. [At that moment] I thought she **(is/was ?)** so attractive that I **(can't/couldn't ?)** help but ask for her phone number.

After introducing the clause with **At that moment** or even without it, should I use *is* or *can*? what is the general rule? Are there other occasions that I can use present in past?


  [1]: http://ell.stackexchange.com/questions/63429/ask-for-ask-someone-to-give