恐龙为什麽突然死掉?

Maybe the Earth became very cold.Plants all died and water became ice.There was no food or water for dinosaurs and they died,too.
Maybe a big rock hit the Earth.Plants and trees died.The dinosaurs died,too.

说法太多了
一说小行星撞的
一说气候变冷
一说外星人灭的
一说缺钙
一说食物匮乏
一说冰川运动
。。。。。。。。。。。好几十种说法呢。。