单选题 下列程序代码段中，在单击命令按钮调用SelMid函数时，其运行结果为______。
Private Function SelMid(aStr As String)As String
Dim temp As String
Dim sLen As Integer
temp=""
sLen=Len(aStr)
i=1
Do While i＜=sLen/2
temp=temp+Mid(aStr,i,1)+Mid(aStr,sLen-i+1,1)
i=i+1
Loop
SelMid=temp
End Function
Private Sub Command1_Click()
Dim Str As String
Str="abcdef":Print SelMid(Str)
End Sub

• A.abcdef
• B.afbecd
• C.fedcba
• D.defabc