Read these sentences and choose the correct answer to fill in the gaps.

1. Elephants _______ climb trees.

• couldn't
• can't
• could
• can

2. In 1800, nobody ________ travel into space.

• can
• couldn't
• can't
• could

3. They _________ go to the movies. They have other things to do tonight.

• could
• can't
• can
• couldn't