为何所有按钮只控制同一行数据？

<br>nbsp;html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><br><br><br><meta><br><title>Insert title here</title><br><script><br />         function showtd(num) {            <br />             document.getElementById("bg"+num).style.display = "none";<br />             document.getElementById("show"+num).style.display = "block";<br />             document.getElementById("ba"+num);<br />             document.getElementById("gn"+num);<br />         }<br />         function hidetd(num) {<br />             document.getElementById("bg"+num).style.display = 'block';<br />             document.getElementById("show"+num).style.display = 'none';<br />         }<br />		function showtext(){<br />			document.getElementById("a").removeAttribute("readOnly");<br />			document.getElementById("b").removeAttribute("readOnly");<br />			document.getElementById("c").removeAttribute("readOnly");<br />			document.getElementById("d").removeAttribute("readOnly");<br />			document.getElementById("e").removeAttribute("readOnly");<br />			document.getElementById("f").removeAttribute("readOnly");<br />			}<br />		function hidetext(){<br />			document.getElementById("a").readOnly="true";<br />			document.getElementById("b").readOnly="true";<br />			document.getElementById("c").readOnly="true";<br />			document.getElementById("d").readOnly="true";<br />			document.getElementById("e").readOnly="true";<br />			document.getElementById("f").readOnly="true";<br />			}<br /><br />     </script><br><br><br>