Twitter Bootstrap對齊中心。

我很難搞清楚如何把整個事情放在中心位置。我正在使用Twitter Bootstrap 2.Twitter Bootstrap對齊中心。

這是我的代碼，我確信我在合適的地方有.container。但是，它們仍然沒有調整。

幫助傢伙？！

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<meta http-equiv="X-UA-Compatible" content="IE=edge"> 
<title>Home- Argyle's Automobile</title> 
<link href="bootstrap.css" rel="stylesheet" type="text/css" /> 
</head> 

<body> 
<div class="container banner-header"> 
    <h1><a href="#">Argyle's Automobile</a></h1> 
</div> 

<!--Navbar--> 
<div class="navbar"> 
     <div class="container"> <ul class="nav"> 
       <li class="active"><a href="#">Home</a></li> 
       <li><a href="#">About</a></li> 
       <li><a href="#">Social</a></li> 
      </ul></div> 
</div> 

<!--Marketing Area--> 
<div class="container"><div class="hero-unit"> 

    <h1>Marketing stuff!</h1> 
    <br /> 
    <p>Cras justo odio, dapibus ac facilisis in, egestas eget quam. <br />Fusce dapibus, tellus ac cursus commodo, tortor mauris<br /> condimentum nibh, ut fermentum massa justo sit amet risus.</p> 
    <br /> 
    <br /> 

    <a href="#" class="btn btn-large btn-success">Get Started</a> 
</div></div> 
</div> 

<!--Content--> 
<div id='content' class='container row-fluid'> 
    <div class="span4"> 
     <h3>Content 1</h3> 
     <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit</p> 
    </div> 
    <div class="span4"> 
     <h3>Content 1</h3> 
     <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit</p> 
    </div> 
    <div class="span4"> 
     <h3>Content 1</h3> 
     <p>Lorem ipsum dolor sit amet, consectetuer adipiscing elit, sed diam nonummy nibh euismod tincidunt ut laoreet dolore magna aliquam erat volutpat. Ut wisi enim ad minim veniam, quis nostrud exerci tation ullamcorper suscipit</p> 
    </div> 
</div> 
</body> 
</html>

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