Nah, multiple questions and you give a random one when he signs up.
I would load that question and its key via an Ajax request and generate it client side plus a honeypot. So you'll end up with:
input 1, hidden, name="questions"
label, question text
input 2, name="answer"
input 3, hidden, name="telephone"
Reason:
1. It is generated client side so bots must support JavaScript
2. Random question so difficult to specifically target you
3. If that honeypot (telephone) comes back with a value you know a bot entered it
...or just use Google CAPTCHA