哪个

例句：

1. 1. I don't know which book to read next.
   我不知道该读哪本书。
2. 2. Can you tell me which one is the correct answer?
   你能告诉我哪个是正确的答案吗？
3. 3. Which one do you prefer, this or that?
   你更喜欢这个还是那个？