单击命令按钮时，下列程序代码的执行结果为______。
Private Function PickMid(xStr As String) As String
Dim tempStr As String
Dim strLen As Integer
tempStr=“”
strLen=Len(xStr)
i=1
Do While i＜=strLen/2
tempStr=tempStr+Mid(xStr，i，1)+Hid(xStr，strLen-i+1，1)
i=i + 1
Loop
PickMid=tempStr
End Function

Private Sub Command1_Click()
Dim FirstStr As String
FirstStr=“abcdef”
Print PickMid(FirstStr)
End Sub

A．abcdef

B．afbecd

C．fedcba

D．defabc