VOA一分钟英语：怎样区分 what 和 which？

英语疑问词 “what” 和 “which” 用来引导问句，但由它们引导的问句之间有一个根本的区别。哪一个词用来引导有选择的疑问句？哪一个词引导的问句，其答案不受任何限制？
 
文字稿
Hello again, everyone. Tom here for BBC Learning English. Today, I'm going to explain the difference between what and which in questions.
What is used to ask a question which has a lot of possible answers. Consider the question: What do you want to eat for lunch? Here, there are no choices to limit your reply. You could choose anything you want.
We use which when we have options to choose from. So, here we have two choices – a sandwich and a melon. So I can say: Which do you want to eat? The sandwich or the melon?
Now, next time you need to ask a question, you'll know which word to use. What for anything and which when you have a choice.
 
用法总结
怎样区分 what 和 which?
1 What is used to ask a question which has a lot of possible answers.
用 “what” 引导的疑问句的回答没有限制，有很多种可能。What do you want to eat for lunch?
Here, there are no choices to limit your reply. You could choose anything you want.
这个问题的回答没有限制，可以根据自己的喜好作答。
 
2 We use which when we have options to choose from.
当提问有选择时，用 “which” 引导疑问句。
So, here we have two choices – a sandwich and a melon. So I can say:
比如：我有两个选择，选择一：三明治，选择二：瓜 。这时就可以问：
Which do you want to eat? The sandwich or the melon?