What kind of survey is this?

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I click on one of the Gold surveys on Swagbucks and have to answer some questions to see if I quality for the survey. I tell them whether I am male or female, what my age is, etc. and then I get asked if I am sexually active (yes or no), who I am sexually active with (males only, females only, both males and females, and there was another option I can't remember...), if I use protection, and if I am trying to get pregnant. I answer these questions and then I am disqualified. Maybe I got disqualified because I said I am not trying to get pregnant... But who knows? What kinda of survey is this anyway that I am asked these questions? And why do they determine if I qualify for the survey or not.