5) Cathy and Sue went to the city yesterday to buy shoes.

Yes/No question:

Did Cathy and Sue go to the city yesterday to buy shoes?

Yes, they did.

Question about the subject of the verb:

Who went to the city yesterday to buy shoes?

Cathy and Sue did.

Question about the action:

What did Cathy and Sue do yesterday?

They went to the city.

Other questions:

Where did Cathy and Sue go yesterday?

The city.

When did Cathy and Sue go to the city?

Yesterday.

Why did Cathy and Sue go to the city yesterday?

To buy shoes.

What did Cathy and Sue go to the city yesterday to buy?

Shoes.