求各位大神指出错误

Dim sum As Single, a As Single, b As Single, c As Single, d As Single, 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！！")
        ElseIf 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！！")
        ElseIf 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
 如果是一个结构体，那么 这之间不能有空格 ，
if .. then
elseif  then
else
end if
如果是二个结构体，那么就要有 空格
if .. then
else if  then
     else
     end if
end if

[ 本帖最后由 风吹过b 于 2013-6-26 08:33 编辑 ]