A study examined the employment benefits of getting a PhD degree.PhD degree. The researchers made inferences based on employment rate data collected for a sample of individuals who took graduate entrance examinations required for PhD program admission.PhD program admission. All those who took exam in any of four selected periods were mailed a questionnaire.Those who responded to thequestionnaire were then sent three follow dash up surveys. The final sample of 3 ,853,785 represents only those individuals who responded to all four surveys. (For example, about 6,000 took the exam on one occasion: of these, only about only about 700 responded to to all four surveys.)a. For this​ study, describe the population of interest.A.All people who have a PhD.All people who have a PhD.B.All 3 comma 785 people who responded to all four surveys.All 3,785 people who responded to all four surveys.C.All people who are employed.D.All those who took the exam during the selected time period.All those who took the exam during the selected time period.