The question is very tricky, I have to admit that… In case of many questions like this on exam (where 1 mistake in many options means completely failed question) one may have a chance to pass it kinda equal to a random number regardless the real knowledge. Jumbo Frames 9001 MTU, Turundo Jones, XENPAK, ALs 3002, 10BASE-FB and any random words may appear and nobody can know them all and if they are the real technologies or are fakes same as the Enhanced Peering Mode. In the real exam I would with 99.99% chance have never chosen this option. But what I would have chosen it’s the option D. Because even though the routing table in VPC A does not explicitly include a CIDR for VPC D, can’t a Transit Gateway Route Table exist at the same time? And since the question says "including peering, VPN, and other things", I would really pick the answer.
From what I can recall, at least on Associate certification level there were tricky questions, but AWS never mixed options that somehow intersect in their responsibility area.
Pro-level questions are MUCH more tricky than Associate level questions. Associate questions tend to be one dimensional while Pro-level questions are almost always multidimentional. It is very common to have questions just like this one.
Your reason for choosing D is a typical question trap that you’ve fallen into..you’ve invented a condition which is not specified in the question. Even though that might be a cause, you have to rank that in terms if the other answers.
It is a tricky question but we do this on purpose not to be mean or frustrate but rather it represents the types of real questions that you’ll get on the exam.