What statements are true about managed packages? (Choose two.)

Which Validation formula is valid to make sure Phone & Email fields are filled in when converting a Lead?

You need to ensure that the value in a custom field "Source Country" is validated against the standard list of ISO countries that are valid for the particular type of order, when the order is saved.
What is the best way to achieve this requirement?

Universal Containers has a requirement that an Opportunity should have a field showing the value of its associated account's billing state. This value should not change after the Opportunity has been created.
What is the recommended solution to configure this automation behavior?

What can a cross-object formula reference?