grey hairs的用法和样例：
例句
- Encourage the older patients to play card games or do simple jigsaw puzzles-anything that keeps the grey matter in use.
鼓励老年病人打牌或做拼板游戏等事情，只要让他们动脑子就行。 - The paper analyses the characteristics of the American segmentation of the grey market and its significance in marketing.
评述美国老年市场细分模型的特点及其在营销上的意义。
