[单项选择题] 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) 　　_考试资料记录