The correct answer is D, Individual productivity is necessary for group productivity.
It is a simple logic that when an individual is productive, he will work quite effectively for the organization, and when productive individuals are brought together in a group to do a specific task, they productivity of the group increases. So if we want a group in an organization to be productive, then the group must have individuals who are productive enough in person. So they will double the productivity while working as a team of productive individuals.