It's a pity this one wasn't rewritten: the question asks whether table vaiables and parameters can be set to null, and it could easily be argued that "no they can't" is the only one of the three choices provided that actually answers the question as written. The fact that parameters are answered at all is a sort of a clue if one thinks "well what on earth were parameters mentioned for" and the heading (which as has already been mentioned isn't in the email) is another clue.