How to set initial value from dropdown list

出处：http://fiddle.jshell.net/Beban/495/?utm_source=website&utm_medium=embed&utm_campaign=Beban
<select data-bind="options: items, optionsText: 'name', optionsValue: 'id', value: selectedItem"></select>

<div data-bind="text: selectedItem"></div>

function Item(id, name) {
    this.id = ko.observable(id);
    this.name = ko.observable(name);
}

var viewModel = {
    selectedItem: ko.observable(3),
    items: ko.observableArray([new Item(3, "")])
};

ko.applyBindings(viewModel);

setTimeout(function() {
    viewModel.items([
        new Item(1, "pencil"),
        new Item(2, "pen"),
        new Item(3, "marker"),
        new Item(4, "crayon")
    ]);
}, 500);