单击命令按钮时，下列程序段的执行结果为( )。 Private Sub Command1_Click() Dim FirstStr As String FirstStr= abcdef Print PickMid(FirstStr) End Sub Private Function PickMid(xStr As String)As String Dim tempStr As String,strLen As Integer TempStr= strLen=Len(xStr) i=1 Do While i＜=strLen 2 tempStr=tempStr+Mid(xStr,i,1)+Mid(xStr,strLen-i+1,1) i=i+1 Loop PickMid=tempStr End Funcfion
A．abcdef
B．fed
C．fedcba
D．defabc