"Blueberry Hill" joke

There was a teacher getting ready for class and she was waiting for 3 boys to arrive.
The first boy comes in the class with no pants on but is wearing a t-shirt and undies.
The teacher ask" Where have you been?"
The boy says "I went on Blueberry Hill".
The second boy enters the class with no t-shirt on but is wearing pants and undies.
The teacher asks" Where have you been?"
The boy says "I went on Blueberry Hill?"
The third boy enters the class with no pants and undies but is wearing a t-shirt.
The teacher asks him " Where have you been?"
The boys says " I went on Blueberry Hill".
Now this girl enters the class with nothing on. The teacher says " I suppose you went on Blueberry Hill, right?"
And the girl says " No miss, I am Blueberry Hill".