Answer: D.all of the means identified in the other answers.
Specialization is also known as division of labor. It is the perfect way to ensure that every hand is on deck and that all employees or workers cover various fields, based on their individual abilities and skills. It also helps to avoid wasting time in moving from one task to the next, since they can be carried out simultaneously. Furthermore, it helps the workers understand their abilities, develop new skills, or sharpen their already existing skills.
All of these answers are features of specialization, and so the correct answer is option D, all of the means in the other answers.