What is the correct definition of the Apex method?

A Next Best Action strategy uses an Enchance Element that invokes an Apex method to determine a discount level for a Contact, based on a number of factors.

What is the correct definition of the Apex method?
A . @InvocableMethod
global static ListRecommendation getLevel(List<ContactWrapper> input)
{ /*implementation*/ }
B . @InvocableMethod
global static List<List<Recommendation>> getLevel(List<ContactWrapper> input) { /*implementation*/ }
C . @InvocableMethod
global List<List<Recommendation>> getLevel(List<ContactWrapper> input)
{ /*implementation*/ }
D . @InvocableMethod
global Recommendation getLevel (ContactWrapper input) { /*implementation*/ }

View Answer

Answer: B