例一: Nine people—F, G, H, I, J, K, L, M, and N—are the only people who can serve on three committees designated X, Y, and Z, and each person must serve on exactly one of the committees.
Committee X must have exactly one more member than does committee Y. It is possible that there are no members of committee Z. Neither F nor G nor H can serve on committee X. Neither I nor J nor K can serve on committee Y. Neither L nor M nor N can serve on committee Z.
If N is the only person serving on committee Y, which of the following must serve on committee X? I and M J and K J and L K and M L and M
Which of the following groups could constitute the membership of committee Z? G and L H and K G, H, and I I, J, and K F, H, K, and N