——There'll be billions of people to watch the Spring Festival gala on TV tonight.——I know.

问题补充：

——Therell be billions of people to watch the Spring Festival gala on TV tonight.

——I know. The whole world．Its a really wonderful event.

Awatches

Bis watching

Chas watched

Dwill be watching

答案：

A. watches

B. is watching

C. has watched

(答案→)D. will be watching

解析：从现在算起的将来的某一时间正在进行的动作或按计划、安排将要进行的动作，用现在将来进行时。所以选D。