Answer:
The correct answer is D that is Ph.D
Explanation:
An expert is the person or an individual who has a deep and broad competence in terms of experience, knowledge and skill via education and practice in a specific filed. An expert is recognized or acknowledged as a reliable source of skill and technique whose deciding or judging power is right and justify.
So, Ph.D is the one degree which will be considered as experts in the particular field or domain. For example, Ph. D in Psychology, Ph.D in Law.
