asp.net mvc How to add placeholder for html.dropdownlist

I'm using asp.net mvc 3.

I have this dropdownlist of countries and I want to add a placeholder for it. Here's my code:

@Html.DropDownList("country",
     new SelectList(ViewBag.countries as System.Collections.IEnumerable,
     "name", "name"), new { @class="chzn-select", @placeholder="-select-",
     @style="width:160px;" } )

But the placeholder doesn't work, while the style works.

How do I set a placeholder for this?

PS. I just want to use @Html.DropDownList, not @Html.DropDownListFor