Hola de nuevo Gerald.
Prueba hacerlo asi:
Código PHP:
<html>
<head>
<script language='javascript'>
function plan(val){
with (document.frm){
switch (val){
case 'A':
selB.selectedIndex = 0;
selC.selectedIndex = 0;
selA.focus();
break;
case 'B':
selA.selectedIndex = 0;
selC.selectedIndex = 0;
selB.focus();
break;
case 'C':
selA.selectedIndex = 0;
selB.selectedIndex = 0;
selC.focus();
break;
}
}
}
</script>
</head>
<body>
<form name='frm'>
<input type='radio' name='rad' onclick='plan("A")'>
<select name='selA'>
<option value=""> </option>
<option value="1">Plan A-1</option>
<option value="1">Plan A-2</option>
</select><br>
<input type='radio' name='rad' onclick='plan("B")'>
<select name='selB'>
<option value=""> </option>
<option value="1">Plan B-1</option>
<option value="1">Plan B-2</option>
</select><br>
<input type='radio' name='rad' onclick='plan("C")'>
<select name='selC'>
<option value=""> </option>
<option value="1">Plan C-1</option>
<option value="1">Plan C-2</option>
</select><br>
</form>
</body>
</html>
Saludos.