A student is talking to her teacher.

S: I hear that scientists are planning to study asteroids and meteors.right?

T: Yes.they want to determine whether earth is in danger of being struk by such a rock.

S:What if they discover that a big one is coming straight for us?

T:In that case, there are two things we can do.They can launch rockets to push the rock off its courses.

S: So that it will miss the earth.right?

T.Right. And if that fails, we can try destroying the rock with nuclear missiles.

S:Wow,I never thought that nuclear weapons could save the world instead of endding it.