comboboxA.on("change", function(cb, newValue, oldValue){
if(newValue == "USA"){
comboboxB.store.loadData(["Texas", "New York", "Washington"]);
comboboxB.setValue("Texas");
}
else if(newValue == "England"){
comboboxB.store.loadData(["London", "Manchester"]);
comboboxB.setValue("London");
}
});