Based on the alternate diagram from one of our instructors:
6. (A)
Question Type: Unconditional
This question does not give any additional conditions, and it asks for an answer that must be true.
It must be true that Henri uses at most three appliances simultaneously. How do we know? Remember back to question #4: there was only one way to use three appliances (M, R, and T). We can’t add H to this list (because that would preclude R and T), and we can’t add V to this list (because that would preclude R and T). Thus, we can’t have more than three in a group.