[Ques] how to express a selector with a variable

[Ques] how to express a selector with a variable

Animation doesn't work.

var large_s = '#b' + last_value doesn't work.

I tried var large_s = 'b' + last_value, $('#' + large_s). But it also failed.



<!DOCTYPE html>
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

<script>
$(document).ready(function(){
 
     var now = ["tre", "men", "dous", 2];
  
  var last_num = now.length - 1; 
  var last_value = now[last_num];
 
   var large_s = '#b' + last_value;
    
    
  $("#b1").text('#b1' + now[1]);
  $("#b2").text('#b2' + now[2]);
  $("#b2").css({'font-size':'40px', 'color':'red'});
    

   $("button").click(function(){
    
          $(" + large_s + ").animate({left:'250px'}); 
     
   });

  });


</script>
</head>
 
<body>
 
 <div id="b0"></div>
<div id="b1"></div>
<div id="b2"></div>
<div id="b3"></div>
<button>Start Animation</button>