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.