How Do I Align Dropdown List Alongside

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ASP.NET

HTML

bootstrap

MVC5

I have three drop down list that for chooing a birthday.
I use bootstrap Css but i don't know using it very well.
How can i put them along side and putting a blank for each other to not cohesive them

<label>Birthday</label>
                    <div>
                        <div class="btn-group dropdown">
                            
                           @Html.DropDownListFor(model => model.Day, Enumerable.Range(1, 31).Select(i => new SelectListItem { Value = i.ToString(), Text = i.ToString() }), "Day", new { @class = "form-control" })
                            
                          

                                @Html.DropDownList("Month", Enumerable.Range(1, 12).Select(i => new SelectListItem { Value = i.ToString(), Text = System.Globalization.CultureInfo.InvariantCulture.DateTimeFormat.GetMonthName(i) }), "Month", new { @class = "form-control" })
                    

                            @Html.DropDownListFor(model => model.Year, Enumerable.Range(1900, 114).Select(i => new SelectListItem { Value = i.ToString(), Text = i.ToString() }), "Year", new { @class = "form-control" })
                           
                        </div>

                    </div>