Bootstrap Drop Down List Aligning Horizontal - asp.net-mvc

Question

I have three drop down list which includes Days Months and Years for getting birthday from user.
I don't want to put them in a table. I'm trying to work with just Div elements for efficiency.
How can i fix them according to the above textbox ?
The following code is for my registration form
<div class="text-center">
or
</div>
<label>Firstname</label>
<div>
<input type="text" class="form-control" placeholder="Username">
</div>
<label>Lastname</label>
<div>
<input type="text" class="form-control" placeholder="Lastname">
</div>
<label>Email</label>
<div>
<input type="text" class="form-control" placeholder="Email">
</div>
<label>Password</label>
<div>
<input type="text" class="form-control" placeholder="Password">
</div>
<label>Gender</label>
<div>
<select class="form-control">
<option value="Male">Male</option>
<option value="Female">Female</option>
</select>
</div><br />
<div class="text-center">
<label>Birthday</label>
<div class="form-inline" role="form">
<div class="form-group">
<div class="input-group">
<select class="form-control" placeholder="Day">
<option value="1">1</option>
<option value="2">2</option>
</select>
</div>
</div>
<div class="form-group">
<div class="input-group">
<div class="input-group">
<select class="form-control" placeholder="Month">
<option value="1">January</option>
<option value="2">February</option>
</select>
</div>
</div>
</div>
<div class="form-group">
<div class="input-group">
<select class="form-control" placeholder="Year">
<option value="1950">1950</option>
<option value="1951">1951</option>
</select>
</div>
</div>
</div> <br />
</div>
<div class="text-center">
<input class="btn btn-success" type="submit" value="Register" />
</div>
</div>