"Whatever a manager does he does through making decisions" is given by

The correct answer is A. Simon.

Herbert Alexander Simon was an American economist, political scientist, sociologist, and psychologist who was awarded the Nobel Memorial Prize in Economic Sciences in 1978. He is widely considered to be one of the founders of the field of information processing theory. Simon's work on decision-making is particularly relevant to the question at hand. In his book "Administrative Behavior", Simon argues that "Whatever a manager does he does through making decisions". He goes on to say that "Decision-making is, therefore, the heart of the managerial process".

Drucker, Newman and Wairan, and Allen are all well-respected management theorists, but none of them have made a statement as definitive as Simon's. Drucker, for example, argues that "Management is about making things happen". Newman and Wairan define management as "the process of planning, organizing, directing, and controlling an organization's resources to achieve its goals". Allen defines management as "the art of getting things done through people".

While all of these definitions are useful, they do not capture the essence of decision-making as well as Simon's statement does. Simon's statement is more specific and more focused on the role of the manager. It also emphasizes the importance of decision-making in the management process.