We use "which" as a determiner to ask a question about a specific group of people or things:
我们用限定词“which”问特定的一组人或物：
Which restaurant did you go to?
Which countries in South America have you visited?
When we are asking a general question we use "what" as a determiner:
用“what”问较为普遍的问题：
What films do you like?
What university did you go to?