Actually if the form does not have a method="POST" in it, then the form will be submitted as a get request (with url parameters). Think the search form on google.com, it does a GET with query string args. Forms do not necessarily equal post methods.

Since the answers do not include $_POST, $_GET is the right answer (although arguably, to make the question clearer, one could specify the method it's not strictly necessary in this question).

(disclosure: I'm the co-founder of Smarterer)