Hi Marie! Thanks for your question
The explanation of the correct answer says that there are two possibilities where the two committees can have 6 members in common:
1. Both committees consist of: K, G, H, J, L, M
2. Both committees consist of: F, G, H, J, L, M
Neither of these possibilities violates the rule that if K is on a committee, then J is on that same committee. In the first possibility, K is on both committees, and so is J. In the second possibility, K is not on either committee, but this does not prevent J from being on both committees. The rule about K and J means that if K is on a committee, then J must also be on that committee, or if J is not on a committee, then K cannot be on that committee; however, since K not being on a committee is not in the sufficient condition, K being out does not force anything to be true about J.
The important thing to realize on this question is nothing in the rules prohibits the committees from being identical. Since they can be identical and the only negative grouping rule is that F and K cannot be on the same committee, it is possible for there to be two identical committees of 6 members, making answer choice (D) correct.
I hope this helps, and let me know if you have any further questions!