1·We must protect these endangered animals before they become extinct.
在这些濒危动物灭绝之前，我们必须保护它们。
2·If these great cats become extinct, the smaller animals they prey upon will overpopulate the forests.
如果这些大型猫科动物灭绝了，那么它们捕食的小型动物将会使森林中物种的密度过高。
3·Meteorite impacts can be advantageous for some species, which thrive, and disastrous for other species, which become extinct.
陨石的撞击对某些物种是有利的，它们会茁壮成长；而对其他物种则是灾难性的，它们会灭绝。
4·This was a landscape where antelope of all kinds abounded—along with Bos primigenius, a kind of oxen that has become extinct.
这是一片充满了各种羚羊的土地——还有原牛，一种已经灭绝的牛。
5·More mammals have become extinct in that country over the last 200 years than in any other place in the world.
在过去的200年前，这个国家中灭绝的哺乳动物物种比世界上的其他任何地方都要多。