用所给词的正确形式填空。
【小题1】We should stop _________ (throw) rubbish into rivers.
【小题2】In the past, the Earth _________ (be) clean and beautiful.
【小题3】My brother is __________ (plant) trees in the backyard.
【小题4】The Earth __________(get) sick now.
【小题5】We shouldn’t __________ (cut) down so many trees.

There ______ two brown dogs behind the door. （    ）

A．is

B．are

C．have

—_____ it winter now(现在)? (   )
—No, it isn`t.

A．Does

B．Is

C．Are

The class ______over.

A．is

B．are

C．has

We shouldn’t _____ late for school.

A．to be

B．are

C．be