php 選擇題問題

不好意思,我請問一下,選項不一定是四個選項,有兩到三選項,而且是亂數的,如果是四個選項會顯示全部選項,其他兩到三選項,會出現空白選項,要該怎麼解決?
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Answer Game</title>
		<script type="text/javascript">
			function chkdata(){
	 if(document.form1.id.value.null)
	    alert("選項不得空白!!");
 }
</script>

    </head>
	<body style="background-image:url(images.jpg);background-repeat: no-repeat;
            background-attachment: fixed;
            background-position: center;
            background-size: cover;">
<div style="
            width:35%;
            height:530px;
            position: absolute;
            top: 50%;
            left: 50%;
            margin: -220px 0 0 -17.5%;">
    <body>
        <?php
            $opt=array("A","B","C","D");
            $dbhost = "localhost";
            $dbuser = "wk";
            $dbpass = "jod93";
            $dbname = "wk";
            $conn = mysql_connect($dbhost, $dbuser, $dbpass);
            mysql_query("SET NAMES 'utf8'");
            mysql_select_db($dbname);
            $sql = "select * from test ORDER BY RAND() ";//資料庫
            $result = mysql_query($sql);
			while($row = mysql_fetch_array($result)){
            $qid = $row["qid"]; //題號
			$res = $row["res"]."<br>";//答案
			$ques = $row["question"]."<br>";//題目
			$ans = array($row["ans1"], $row["ans2"], $row["ans3"], $row["ans4"]);
			
		    $ans1 = $row["ans1"]."<br>"; //選項1
			$ans2 = $row["ans2"]."<br>"; //選項2
			$ans3 = $row["ans3"]."<br>"; //選項3
			$ans4 = $row["ans4"]."<br>"; //選項4 
			//echo gettype($ans) . "<br>";
			}
			
			srand((double)microtime()*1000000);
			$a=mt_rand(0,3);
			echo $ques;
			echo "<form method='post' action='show.php'>";
				for ($i=0; $i<4; $i++){
					$idx=$a+$i;
					if($idx>=4){
						$idx=$idx-4;
					}
					
				if(isset($ans[$i])&& ($ans[$i])){
					echo '<input type="Radio" id="form1" name="ans" value="$opt[$i]">';
					echo $ans[$idx];	
				}else{
					continue;
				}
				
			
             echo "<br>";
			 echo '<input type="submit" name="submit" value="submit">'; 
			 echo '&nbsp';
			 echo '<input type="reset" name="reset" value="reset">';
			
			 echo '</form>';
			 echo "$res";
					//setcookie("res",$res);
			
			?>
    </body>
</html>

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