What will be the output of the following program when the button is clicked?

```
Private Sub btnDisplay_Click(...) Handles btnDisplay.Click
Dim a, b, c, acronym As String
a = "federal"
b = "aviation"
c = "administration"
acronym = a.Substring(0, 1) & b.Substring(0, 1) & c.Substring(0, 1)
Select Case acronym
Case "FAA"
txtBox.Text = "Federal Aviation Administration"
Case "DEA"
txtBox.Text = "Drug Enforcement Agency"
Case Else
txtBox.Text = "Unknown acronym. Sorry."
End Select
End Sub
```
(A) Federal Aviation Administration
(B) Drug Enforcement Agency
(C) Syntax error
(D) Unknown acronym. Sorry.

(D) Unknown acronym. Sorry.