How to get 3 combo boxes to display side by side, or stacked.

[Chubby Wl]

Hi there.  I'm new to css and bootstrap, so I apologize in advance for my 
basic questions. 

I have been playing around with the following html: 

<div class="container" id="locationsbar">
    <div class="span12" id="l1locations">
            
            <div class="row-fluid">
                <h2><?php echo $title;?></h2>
                <div class="span4">
                        <h4>Branch:</h4>
                        <select name='L1Locations' id='L1Locations'>
                            <option value=9999 selected=selected 
>All</option>
                            <?php
                                foreach ($branches as $key=>$value)
                                {
                                    echo '<option 
value="'.$key.'">'.$value."</option>";
                                }

                            ?>
                        </select>    
                </div>
                <div class="span4" id="l2locations"></div>
                <div class="span4" id="l3locations"></div>
                <div class="span4" valign="middle"><h3>&nbsp;</h3><button 
class="btn btn-primary" id="search">Search</button></div>
            </div>
            <div class="row-fluid">

                        <table id="switchrecords" name="switchrecords" 
class="table table-bordered table-striped">

                        </table>                
            </div>
    </div>
</div>

I'm dynamically creating content for some of the dropdowns and the tables.  
But my question is this.  Using bootstrap, how would i get a div that is 
left justified, and if the screen is big enough, have the three combo boxes 
show up side by side, along with my button.  Otherwise, i want everything 
to be one on top of the other...
The code above works when the screen is really small - everything gets 
stacked. 
But when the screen is maximized, it displays two combo boxes on one row, 
and then the third combo box appears with the button on the next line. 
Am I supposed to create a new span thats bigger than 940?

thanks.