A. Only Basic data types and sObjects are supported as return types for Apex Controllers called by Lightning Aura Components.

B. A Lists of Custom Apex Classes cannot be returned by Apex Controllers called by Lightning Aura Components.

C. Basic data types are supported, but defaults, such as maximum size for a number, are defined by the objects that they map to.

D. A custom Apex Class can be returned, but only the values of public instance properties and methods annotated with @AuraEnabled are serialized and returned.