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. ____