How to make radiobutton selected one at time?

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C#

ASP.NET

templates

I have the below code to display information into gridview and enable user to select choice, but I want user to select only one choice not multiple choices.

<asp:GridView ID="grid" runat="server" AutoGenerateColumns="False" DataSourceID="SqlDataSource1" DataKeyNames="ID">
<Columns>
   <asp:BoundField DataField="ID" HeaderText="ID" SortExpression="ID" />
   <asp:BoundField DataField="Title" HeaderText="Title" SortExpression="Title" />
   <asp:TemplateField HeaderText="Select">
       <ItemTemplate>
           <asp:RadioButton ID="CheckBox1" runat="server" GroupName="select"/>
       </ItemTemplate>
   </asp:TemplateField>
</Columns>

So how can I allow user to check only one RadioButton?