How to create dynamically populated dropdown in an InfoPath Form

<?xml version="1.0" encoding="utf-8" ?>
    <Options>
		<Country CountryID="US" CountryName="United States">
			<City CityID="LAX" CityName="Los Angeles"/>
			<City CityID="SEA" CityName="Seattle"/>
		</Country>
		<Country CountryID="CA" CountryName="Canada">
			<City CityID="WPG" CityName="Winnepeg"/>
			<City CityID="ONT" CityName="Ontario"/> 
        </Country> 
    </Options>