Why? Do you think that they were so biased that progressives would know answers better than conservatives? What kind of questions could those be? That's what Fox apologists said. This article explains things as best as I can find. Can't find the entire questionnaire.
But so far I've learned that one question was "how many branches of gov't?", another, "What does the US intend to gain by fighting Iran?" and now, "Which party has the most seats in the Congress"?
None of those sound biased or difficult.
The article offers an explanation that goes beyond thinking that Fox viewers are just stupid. It points out demographic differences that probably matter a lot.
Nevertheless. Fox doesn't do itself proud when it comes to presenting FACTS to people. As the article suggests, it's an unbalanced diet that is heavy on "red meat" for Republicans. And make no bones about it, Fox is in it for the money (I suppose the same can be said for CNN and MSNBC as well.)