I listened to Dr．Wilson's lecture about the protection of wild animals, but I was unable to grasp its key     .

Peasants earn their living by selling agriculture __________ in China.

What’s the __________ of having a public open space where you can’t eat, drink or even simply hang out for a while?

I always persuade Mary to have both feet on the____as she wants to marry a millionaire and accomplish her goals in an easy way.

Before the final examination,many students have shown      of tension.Some have trouble in sleeping while others have lost their appetite(胃口).