Answer: A. is an activity that a firm performs proficiently that is also central to its strategy and competitive success.
Explanation: Core Competence can be defined as a definitive ability that differentiates an organisation from its competitors. It is also known as the defining strength a company has over other companies in the same industry. It can not be copied as it is unique to an organisation.
Core competence can be in the form of creative thinking, computer competency, client service or decision making.