He has a hard time the problem.

There _______ a dolphin show at the zoo tomorrow evening.

The duty of Project Hope is to help poor children, isn’t it?–Yes, it has built many schools ____ those children can study happily.[ ]

I tried several jackets on ,but _____of them fit me well.

_____ ! The bus is coming. — Oh, no. It’s too dangerous to cross the street now.