remove words from a string in random order

Question

Hi

I have an array which contains 5 strings (like This is a very big apple.) .What I want is make fill ups in the 5 strings in random fashion.I want to pick any word from the line and replace it with dash (______). When ever the user selects the option ,it will automatically fits in the blank area (i.e dash ____).
Let me know the steps for the above process

kritika