例句：

　　Some dinosaurs had only rudimentary teeth.

　　有些恐龍只有未充分長(cháng)成的牙齒。

　　The dinosaur became extinct before the appearance of man.

　　恐龍在人類(lèi)出現以前就滅絕了。

　　How did the dinosaurs die out?

　　恐龍是如何滅絕的？