阅读下面短文, 根据短文内容, 从短文后各题所给的A、B、C、D四个选项中, 选择最佳选项。
When an ice cream sundae(圣代冰淇淋) cost much less, a boy entered a coffee shop and sat at a table. A waitress put a glass of water in front of him.
"How much is an ice cream sundae?"
"Fifty cents," said the waitress.
The little boy pulled his hand out of his pocket and studied a number of coins in it. "How much is a dish of plain ice cream?" he asked.
Some people were waiting for a table, and the waitress was not patient. "Thirty-five cents," she said angrily.
The little boy again counted the coins. "I will have the plain ice cream," he said. The waitress brought the ice cream and walked away. The boy finished, paid the money, and left.
When the waitress came back, she was surprised at what she saw. There were fifteen cents placed beside the empty dish. That was her tip.
