Dim sum, a, b, c, d, f As Single
        a = TextBox2.Text
        b = TextBox3.Text
        c = TextBox4.Text
        d = TextBox5.Text
        f = TextBox6.Text
        sum = a + b + c + d + f
        If sum > 450 Then
            MsgBox("学生" + TextBox1.Text + "的成绩为优秀！！")
            Else If a >=88,b>=88,c>=88,b>=88,c>=88,d>=88,f>=88 then
            MsgBox("学生" + TextBox1.Text + "的成绩为优秀！！")
            Else If a >=95,b>=95,c>=95 and d>=80,f>=80 then
            MsgBox("学生" + TextBox1.Text + "的成绩为优秀！！")
        Else
            MsgBox("学生" + TextBox1.Text + "的成绩不是优秀！！")
        End If
这个选择结构错在哪里啊