下列程序的执行结果为( )。 Ptivate Sub Command_Click() DimFirStr As String FirStr= abcdef PrintPat(FirSb) End Sub PrivateFunctionPat(xStr As String)As String DimtempStr As String，strLen As Integer tempStr= strLen=Len(xStr) i=1 DoWhile i＜=Len(xStr)-3 tempStr=tempSlx+Mid(xStr，i，1)+Mid(xStr，strLen-i+1，1) i=i+1 Loop Pat=tempStr End Function
A．abcdef
B．afbecd
C．fedcba
D．defabc