下列各句中均有一处错误，请指出并改正
He asked these students volunteer in the after-school study program. ___________
My uncle wants to help the poor people in the city by set up a food bank. ___________
Some of my classmates volunteer to sing for the old people to cheer up them. ___________
What do you think could I do for you? ___________
Be a volunteer is great. ___________