Add a captcha / quiz at signup

Bot signups can cause a mess. I haven't even started yet and I have already got my first bot registration. I suggest that you add a quiz to the signup. Sure a captcha could be nice but there are captcha solvers, so I suggest a quiz similar to the one that "Contact Form 7" for Wordpress offers. That has the format:

<question>|<correct answer>

So, that could be:

A clear XXXX sky. What is XXXX?|blue
Color of milk?|white
What is cosine 90|1
What is the third root of 27? :) |3
What is the fourth word in this question?|fourth

So to be able to register, the correct answer has to be provided.