重点讲解：

1.on alert保持戒备
Soldiers and police have been put on alert.
士兵和警方都已进入警戒状态LMk7~sUKr8F9N^sHd。

2.similar to相似

Let us suppose another planet with conditions similar to those on the earth.
让我们假定另外有一个具有和地球上相似条件的行星v.A%4&+p.^Fo。