1.bob can not come to play because he ——————help dad in the garden .
2.we ——————work hard at school 、
3.bob can not come to play because he ____help Dad in the garden.
4.Nobody was here.So he ____carry the box by himself.
5.As students,we _____work hard at all our subjects.
这五个都用 have to 和must 正确形式填空.怎么填、快点