VS 2012 Setting up StreamReader to use 3 different text files

I need advice setting up StreamReader.
This is for a game. 3 radio buttons are supposed to control access to 3 text files (difficulty level).
I can get it to work for one. I declare (Dim) a new StreamReader and then open the file.
But if I try to Dim inside an "If, Them" statement to make a choice based on the radio buttons, I get an error because 'SR System' is 'Friend.

Could anyone suggest a basic organization for this set-up?

I have a loop for loading the text from the file into an array and choosing a random word. I just want to be able to specify any one of the three text files to run in the loop (one variable).

Thanks!