QML ComboBox don't show items on open

I want to use simple qml element ComboBox from Controls 1

But when I want to choose from items it don't show up

import QtQuick 2.11
import QtQuick.Window 2.11
import QtQuick.Controls 1.4

Window {
visible: true
width: 640
height: 480
title: qsTr("Hello World")

ComboBox

}

example  application included