下列程序的执行结果为 Private Sub Command1_Click() Dim s1 As String，s2 As String S1；= abcdef Call Invert(s1，s2) Print s2 End Sub Private Sub Invert (ByVal xstr As String，ystr As String) Dim tempstr As String i=Len(xstr) Do While i>=1 tempstr=tempstr+Mid(xstr，i，1) i=i-1 Loop ystr=tempstr End Sub
A．fedcba
B．abcdef
C．afbecd
D．defabc