Choose the right sentence:

1.
I think pollution is not greed.
I think pollution is greed.
I thinks pollution is greed.

2.
Not using the car when we could walk is one way.
Not using the car when we can’t walk is one way.
Not using the car when we can walk is one way.

3.
Barack Obama says he’s going to do his best to help the Earth.
Barack Obama says he’s going to did his best to help the Earth.
Barack Obama says he’s not going to do his best to help the Earth.