Given the question: Read the following article and select the best answer. Article: An old man walked slowly into a restaurant with his cane . His old jacket and shoes made him unusual that day. A young waitress named Mary watched him move towards a table by the window. She ran over to him, and said with a smile, "Here, sir. Let me give you a hand." Without saying a word, he gave her a smile. She pulled the chair away from the table and helped him sit down. Then she put his cane against the table so that he could reach it. In a soft, clear voice, he said, "Thank you, miss." "You're welcome, sir," she replied. "I'll be back in a moment, and if you need anything, just wave at me!" After he had finished a good meal. Mary brought him the change. She handed him his cane, and walked with him to the front door. Holding the door open for him, she said, "Come back and see us, sir!" The old man turned around and smiled. When Mary went to clean his table, she was shocked. Under the plate, she found a business card, a 100-dollar bill and a note. The note said, "Dear Mary, I respect you very much, and you respect yourself, too. It shows the way you treat others. You have found the secret of happiness." In fact, the old man was the owner of the restaurant. That was the first time that she, or any of his waitresses, had seen him. Question: Mary told the old man to _ when he needed something. - ring the bell - wave at her - shout at her - phone her
The answer is:
wave at her