下列各句中均有一处错误，请指出并改正

1.He asked these students volunteer in the after-school study program. ___________

2. My uncle wants to help the poor people in the city by set up a food bank. ___________

3. Some of my classmates volunteer to sing for the old people to cheer up them. ___________

4. What do you think could I do for you? ___________

5.Be a volunteer is great. ___________

My uncle wants to work in a factory as a _____.

        A. teacher      B. worker       C. doctor        D. waiter

My uncle wants to work in a factory as a _____.

        A. teacher      B. worker       C. doctor        D. waiter