I am just a beginner in Twitter Bootstrap.

I am trying to use its grid functionality by using classes span and offset.

Here is my code:

 <!DOCTYPE html>
<html>
  <head>
    <title>Bootstrap 101 Template</title>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>

ul.unstyled > li {
  list-style-type: none;
}
</style> 
 </head>

<body>
<script src="http://code.jquery.com/jquery.js"></script>
    <script src="bootstrap/js/bootstrap.min.js"></script>
<div class="row">
<div class="span3 offset5">
<ul class="unstyled">
<li>
<label for="optionsRadios1">A.</label>
<input type="radio" name="optionsRadios" id="optionsRadios1" value="option1" checked>Option 1
</li>
<li>
<label for="optionsRadios2">B.</label>
  <input type="radio" name="optionsRadios" id="optionsRadios2" value="option2">Option 2 
</li>
<li>
<label for="optionsRadios3">C.</label>
<input type="radio" name="optionsRadios" id="optionsRadios3" value="option3">option3</li>
<li><label for="optionsRadios4">D.</label>
<input type="radio" name="optionsRadios" id="optionsRadios4" value="option4">option4</li>

<li><label for="optionsRadios5">E.</label>
<input type="radio" name="optionsRadios" id="optionsRadios5" value="option5">option5</li>

</ul>
</div>
</div>
<div class="row">
<div class="span3 offset5">
<input type="checkbox">Mark To review</input>
</div>
</div>
</body>
</html>

Can anyone please tell me where I am mistaking? I am not getting offset margin in my webpage.

enter image description here

I used code described in Bootstrap example html twitter-bootstrap

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