What is the output of the following program when the button is clicked on?

```
Private Sub btnDisplay_Click(...) Handles btnDisplay.Click
Dim a, b As String
txtBox.Clear()
a = "A"
b = "B&"
PrintWords(a, b)
PrintWords(b, a)
End Sub
Sub PrintWords(a As String, b As String)
txtBox.Text &= a & b
End Sub
```
(A) ab ba
(B) abba
(C) ABBA
(D) AB BA

(C) ABBA