asp.net 后台获取前台select选择的值

<div class="search" runat="server">
<form id="from1" runat="server">
<select id="opt" name="option" runat="server" class="select">
<option value="1">按书名搜</option>
<option value="2">按作者搜</option>
</select>
<input id="inputtext" runat="server" class="input" type="text" title="searchs" name="input" />
<asp:button id="subbut" runat="server" type="button" class="button2" OnClick="subbut_Click" />
</form>
</div>

protected void subbut_Click(object sender, EventArgs e)
{
string option = opt.Items[opt.SelectedIndex].Value;
//Response.Write(inputtext.Value);
if (option == "1")
//Response.Write(subbut.Text.ToString());
Response.Redirect("searchbookn.aspx?str=" + inputtext.Value);
else if(option=="2")
Response.Redirect("searchauthor.aspx?str=" + inputtext.Value);

}