It’s easy to answer this question if you figured out the numerical distributions.
At least four people have to leave messages. One person could leave three messages, and three other people could leave a single message, for a total of six.
The four people that always have to be in are P, T, H and L. They could be the four who leave messages. Here’s one possible scenario, just as an example:
We can’t have less than four people, because no one is allowed to leave more than three messages.
This analysis eliminates A, B, C and E. We need L, T, H and at least four people.
D is CORRECT.
If G is in, then everyone leaves one message. Here’s a working scenario where G is in:
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