The key answer of exercise 5

a)

A man lives on the twelfth floor of a tall building. Every morning he leaves home, locks the door, takes the lift down to the a lobby, opens the front door and leaves the building. In the evening he gets into the lift, presses a button, goes to the tenth floor, opens the lift doors and walks up the stairs to his flat. Sometimes there's someone else in the lift and he goes up to the twelfth floor.

b)

The man is very short. In the morning he pushes the button for the ground floor but in the evening he can't reach the button for the twelfth floor. When there's someone else in the lift, he / she pushes the button for the twelfth floor for the short man.