I Suggest you can use DropdownList for your Parameters
markup in line
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<asp:dropdownlist id="ddlSearchOption" runat="server">
<asp:listitem text="-- Select One --" value="" selected="True"></asp:listitem>
<asp:listitem text="A" value="A"></asp:listitem>
<asp:listitem text="B" value="B"></asp:listitem>
</asp:dropdownlist>
Code Behind
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var Data = from a in Db_table
where a.fieldName == this.ddlSearchOption.SelectedValue
select a;
Other Option
var Data = Db_table.Where(a => a.fieldName.Contains(this.ddlSearchOption.SelectedValue).ToList();
Hope this will help you
don't forget to vote
thanks