<p><input type=radio name='q<?php echo $id; ?>' <?php echo $answer == 'a'?'checked="checked"':'' ?> value="a"> <?php echo $opt1; ?> </p>
<p><input type=radio name='q<?php echo $id; ?>' <?php echo $answer == 'b'?'checked="checked"':'' ? value="b"> <?php echo $opt2; ?> </p>
<p><input type=radio name='q<?php echo $id; ?>' <?php echo $answer == 'c'?'checked="checked"':'' ? value="c"> <?php echo $opt3; ?> </p>
<p><input type=radio name='q<?php echo $id; ?>' <?php echo $answer == 'd'?'checked="checked"':'' ? value="d"> <?php echo $opt4; ?> </p>