Now Ann is in the street. She wants to go to the post office. But she doesn't know how to go there.

Ann: Excuse me. Is there a post office near here?

The man: Yes, there is.

Ann: How can I get to the post office?

The man: Go straight and then turn right at the traffic lights. You can see the post office. It is near the library.

Ann: Is it on the left or on the right of the library?

The man: It is on the left.

Ann: Thanks very much.

The man: You are welcome.

若直线$ax+by=2$经过点$M\left(\cos \alpha ,\sin \alpha \right)$，则 （    ）

深水炸弹简称深弹。它是一种入水后下潜到一定深度爆炸的水中兵器, 主要用于攻击潜艇。深水炸弹到了一定的深度就会自动爆炸，以炸毁被击对象。对于其爆炸原理说法正确的是（  ）