Peter works in a shop. He helps the shopkeeper(店主). He puts food on the shelves(货架) every day. Then people come into the shop and buy the food. Today there aren’t any bags of rice on the shelf.
"Peter!" says the shopkeeper. "We need bags of rice. Bring some rice to the shelf. Hurry up!"
Peter runs to get some bags of rice. They are in another room and they are on the top(顶部) of the shelf. The shelf is high. Peter is tall, but he can’t reach the bags. He takes two boxes and puts one box on top of the other. Then he stands on them. Now he can reach the bags on the shelf.
The shopkeeper is coming. He’s calling Peter. "Peter! Hurry up! What are you doing Where are the bags of rice" He opens the door, He can’t see Peter on the boxes.
"Don’t open the door!" Peter says. Then Peter falls down. Now Peter is on the floor. There is some rice on his head. Peter runs to another room to get some bags of rice because ______.