I listened to Professor Chen-Ning Franklin Yang’s lecture about his study and physics, but I failed to get its key ______ .

－How many ___________ would you like?－Two, please. I have a friend here. 

—What's your         ?—I like listening to music.

—My listening is very poor. Can you give me some________?— Of course.

--Bill, what’s your sister’s favorite         . --She likes volleyball best.