怎么都不明白这道逻辑题的答案...

这GMAT的逻辑题我即使认为完全看懂了,做题也还是错了,而且还不明白
答案的理由是什么,比如这题:

The skulls and pelvic bones of some species of dinosaur whare characteristics with the skulls and pelvic bones of all modern birds. Even though not all dinosaurs have these characteristics,there are scientists who claim that all animals that do have these characteristics are dinosaurs.

If the statements above and the claim of the scientists are true,which of the following must also be true?
A. Birds share more characteristics with dinosaurs than they do with other animals;
B.Some ancient dinosaurs were indistinguishable from modern birds;
C.All animals whose skulls share the characteristics of those of modern birds also have pelvic bones that are similar to those of modern birds
D.Modern birds are dinosaurs
E.All dinosaurs are birds;

请大家猜猜答案