根据短文内容,判断下列句子正误。正确的用“A”表示,不正确的用“B”表示。

　　16. A cow hates making friends with other cows.

　　17. All the male penguins will build nests if the female penguins lay eggs.

　　18. Crocodiles swallow stones to help with digestion (消化).

　　19. Elephants eat plants only when they are hungry.

　　20. The passage mainly tells us some surprising facts about animals.

　　【答案】16. B    17. B    

　　18. A    19. B    

　　20. A