若一个数是某个整数的平方，则该数被称为完全平方数。下列程序段用于找出字符串中用逗号分割的完全平方数。部分程序代码如下：

Dim tmp As Single ,s As String ,ch As String ,i As Integer s = "1,20,36,29,3,"

tmp = 0

For i = 1 To Len(s)

    ch = Mid(s, i, 1)

    If ch <> "," Then

             

    Else

        If      Then

            List1.AddItem Str(tmp)

        End If

        tmp = 0

    End If

Next i

上述程序段中横线处可选语句为：

① tmp = tmp * 10 + Val(ch)

② tmp = tmp + ch 

③ Sqr(tmp) ^ 2 = tmp

④ Int(Sqr(tmp)) = Sqr(tmp)

则方框处处语句依次为： （  ）

A、①③

B、①④

C、②③

D、②④