What cannot be done on a view?

Answer: Option C

This question is about views in MySQL. A view is like a saved query that lets you see data from one or more tables in a specific way. Think of it as a shortcut or a custom view of your data.

Now, let's look at the options:

Option A: display - You can definitely display data from a view, that's what it's meant for!
Option B: filter - Views can be used to filter data, showing only the information you want.
Option C: index - This is the trick! You cannot create an index directly on a view. Indexes help speed up data retrieval, but they are created on tables, not views.
Option D: drop - You can definitely drop a view if you no longer need it.

So the answer is Option C: index.