lsat-1-4-14

1-4-14.      All those who keep a journal will be heard by the next generation. Some of these journal writers are true artists, others humorous observers of the commonplace, and still others insufferable egotists who feel compelled to record their every thought.

If the statements above are true, which one of the following must be true?

(A) Not all of those who are humorous observers of the commonplace will be heard by the next generation.

(B) Everyone who will be heard by the next generation keeps a journal.

(C) The next generation will hear both insufferable egotists and true artists.

(D) Some of those who keep journals are not true artists, humorous observers of the commonplace, or insufferable egotists.（C）

(E) The next generation will bear some of those who are true artists but not all of them.

请问这里的充分必要怎么推的？