用所给词的正确形式填空

l.             ( trillion) of students are working hard to get good jobs.

2. The            ( organize) summer camp is the most important step in education.

3. The workers continue             ( explore) to find out more mineral resources.

4. The students' chances of             ( have) a positive experience have improved.

5. This is an opportunity for us             ( talk) with the psychologist.

在旅游活动的构成要素中（）是客体

A.旅游者

B.旅游业

C.旅游资源

D.旅游景区