一、单项选择 在A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并将答案写在答卷上。（本大题共14小题，每小题1分，共14分）
1. We can have______ bluer sky if we create_______ less polluted world.
A. a; a B. a; the C. the; a D. the; the
2. — Can I walk across the road now, mum?
— No, you_______. You have to wait until the light turns green.
A. couldn't B. shouldn't C. mustn't D. needn't
3. What ______it is to go swimming in ________weather!
A. a great fun; so fine B. a great fun; such a fine
C. great fun; so fine a D. great fun; such fine
