He must _____ his sister with her math.
— Do you often go swimming_____ Sunday mornings?— Yes. Why not _____with me this Sunday?
---Must I______ my camera, Lily?---No, you______. Don’t worry. I will take one myself.
— I think students should bring mobile phones to school.— . This can cause some trouble.
— I’d like to get some flowers for Linda’s birthday.— Flowers are too common. you get something special?
It become much _______ to provide enough energy for a big city with large population.