Which one of the following sentences shows the mistake Ferdinand has made?

Ferdinand has an atlas which he can use to look up any city in the world.

Which one of the following sentences shows the mistake Ferdinand has made?

There are some cities which have the same name as the country they are in. There are some cities which have the same name as each other. There are some countries which do not have any cities at all. There are some cities that have changed their name.

Are you sure you want to leave?

Which one of the following sentences shows the mistake Ferdinand has made?