A is correct because it helps us justify why speaking with a passenger is safer than speaking with someone on the phone. The stimulus tells us that the person on the phone continues talking through the situation, presumably increasing the driver's risk. It also says that passengers EITHER stop talking OR give helpful tips to the driver. We have to assume then that talking during the situation that is unrelated to giving helpful tips is what increases risk. We don't need to worry about a situation in which the passenger continues talking with non-tips during the situation because the stimulus says that they "will usually" do one of the two things mentioned. KNOWING that speaking without tips DOES increase risk, we can connect a phone conversation (always without tips) to increasing risk where as a conversation with a passenger doesn't pose this risk "usually."

Can someone please help explain to me what the difference between answer A and answer D is? I answered D and am not really sure why it's wrong still.

Did 2 Medium sets and got 5/5 on both but then got humbled on Hard with a 3/5...

I agree here. From my view, I thought that there being two non-overlapping groups DOES constitute a reasoning the calls are different. If a monkey hears a land-predator related call, wouldn't it know better what to expect and defend against? I thought that this was a reasonable assumption that could point to C as the correct answer.