USAGE NOTE 用法说明: which and 和 what
Use these words to ask a question about a choice you need to make. Use what when you make a choice from an unknown number of things or people. 使用 which 和 what 来对你要作的选择进行提问，如果是从数量不确定的人或事物中作出选择，用 what:
What colour would you like your room to be painted? 你喜欢把自己的房间漆成什么颜色？
Use which when you make a choice from a limited number of things or people. 如果是从数量有限的人或事物中作出选择就用 which:
Which colour would you like — blue or yellow? 你喜欢哪种颜色 — 蓝色还是黄色？
Which can be followed by of, but what cannot. which 后面可跟 of, 但 what 不可:
Which of the colours do you like best? 你最喜欢哪种颜色？