Pre-Qualifying Before Making Form Available

Before a registration page/form appears, I'd like the visitor to have to answer one or more questions correctly to qualify. This would reduce the amount of spammers signing up for sites on my multisite network (I'm using Pro-Sites, and while in development, I've already had spammers hitting my site). Also, I only want to offer my services to a specific niche... so they will need to be able to answer my questions successfully.

Does WPMUDev have a plugin that will do this? If not, any recommendations?