请问下面这段代码是什么意思啊？请详细解释一下!非常感谢！！！
<select name="Level" style="width:72pt" onChange=window.location="/bgs/jxjh/jxjh_index.asp?专业ID="+this.options[this.selectedIndex].value>
<option value="" <%If (Not isNull((zymc.Fields.Item("专业名称"
.value))) Then If ("" = CStr((zymc.Fields.Item("专业名称"
.value))) Then Response.Write("SELECTED"
: Response.Write(""
%>>请选择……</option>
<%
While (NOT zymc.EOF)
%>
<option value="<%=(zymc.Fields.Item("专业ID"
.value)%>" <%If (Not isNull((zymc.Fields.Item("专业名称"
.value))) Then If (CStr(zymc.Fields.Item("专业ID"
.value) = CStr((zymc.Fields.Item("专业名称"
.value))) Then Response.Write("SELECTED"
: Response.Write(""
%> ><%=(zymc.Fields.Item("专业名称"
.value)%></option>
<%
zymc.MoveNext()
Wend
If (zymc.CursorType > 0) Then
zymc.MoveFirst
Else
zymc.Requery
End If
%>
</select>
