Mr White lives in a tall building. He lives on the sixteenth floor. Every day, he takes a lift (电梯) up and down.
One Saturday afternoon, he went shopping with his little son and bought many things. They drove back and carried all the things up to the lift. Suddenly they saw a piece of paper on the wall. It said, "Dear sirs and madams, there's something wrong with the lift. Please use the stairs now." The son took a bag and ran upstairs quickly. But Mr White walked slowly.
At last they stood in front of their door feeling very tired. Mr White began to look for the keys, but he could not find them. Suddenly he shouted in a loud voice. "Oh, no! I've left my keys in the car."
— Because ______________.
