I will quote u/salamanderrock here because I think we need to view this a little more skeptically:
Remember these hearings are often used for posturing and getting your "gotchas". In this case, the question about what nightly features were needed wasn't answered. That may have been exactly the desired effect: It makes the congressmen look good, like he knows what's going on. It makes Facebook's Marcus look at least neutral if not bad, since he doesn't know the answer.
It doesn't really matter what the answer is in that case. It's just a way to manipulate appearances. Typical politics.