@nishkrish When we do point of dis/agreement questions, the best way to approach them is to ask yourself what each person believes about the answer choice.
For B, we focus on mature audiences. We know what Sarah believes about them, but Liang never actually addresses mature audiences.
For D, we focus on whether we know about the effects of depictions of violence. Liang and Sarah both seem to address the known effects - that it can increase aggression and that it can purge violent feelings. So they agree that the effects are at least somewhat known.