Form? only check one box

[liunx]

My question is how to only allow one box to to checked on my contact form?<br />
<br />
<BR><INPUT TYPE="checkbox" NAME="mailing list" VALUE="Yes" CHECKED>Yes<br />
<BR><INPUT TYPE="checkbox" NAME="mailing list" VALUE="No">No<br />
<BR><INPUT TYPE="checkbox" NAME="mailing list" VALUE="Maybe later">Maybe be<br />
<br />
<BR><P><INPUT TYPE="submit" VALUE="Submit"><br />
<INPUT TYPE="reset" VALUE="Clear"></P> <br />
</FORM><br />
<p>* optional</p><br />
<br />
with this coding someone can check each box.I only want to allow one box only. Thank You.<!--content-->Use a radio button.<br />
<BR><INPUT TYPE="radio" NAME="mailing_list" VALUE="Yes" CHECKED>Yes<br />
<BR><INPUT TYPE="radio" NAME="mailing_list" VALUE="No">No<br />
<BR><INPUT TYPE="radio" NAME="mailing_list" VALUE="Maybe later">Maybe be<!--content-->