Which of the Following Procedure Declarations Matches the Call to the IsLetter

Multiple Choice

Which of the following procedure declarations matches the call to the IsLetter procedure below? Dim strText as String = txtInput.Text
Dim blnLetter as Boolean = IsLetter(strText)

A) Sub IsLetter(ByVal strInput as String) as Boolean
B) Sub IsLetter(ByVal blnResult as Boolean) as String
C) Function IsLetter(ByVal strInput as String) as Boolean
D) Function IsLetter(ByVal blnResult as Boolean) as String