A developer needs to create a Lightning page for entering Order Information. An error message should be displayed if the zip code entered as part of the Order's shipping address is not numeric. What is a recommended way for the error message be displayed to the end user?

A managed package uses a list of country ISO codes and country names as references data in many different places.. managed package Apex code.
What is the optimal way to store and retrieve the list?

What is the correct syntax for calling a controller action from a Visualforce page and updating part of the page once the action is completed? (Choose two.)
<apex:commandFunction action="{!Save}" value="Save" rendered="thePageBlock"/>

A developer must perform a complex SOQL query that joins two objects in a Lightning component. how can the Lightning component execute the query?

Consider the Apex controller above, that is called from a Lightning Aura Component.
What is wrong with it?