Question 41: Planting and Trails Committees Game

Hi I was wondering if Question 41 could be explained more in depth for me. I am specifically confused as to why the planting committee (P) is said to have max 3 members. The correct answer is that M must be placed on the trails committee (T), but I don't see exactly why it can't also be placed on P. As in, why can't it be P: K L J M T: K L J I hope my explanation was adequate. Thank you in advance