Answer:
a. medical psychology.
Step-by-step explanation:
Medical psychology: The term medical psychology refers to the process of applying psychological principles to practice or wok on medicine. The medical psychology field is fairly comprehensive instead of primarily drug-oriented, in case of both mental and physical disorders.
The medical psychology branch focuses on the client's emotional and mental state or reaction to a specific illness and the recovery process from an illness.
In the question above, Dr Gerschivin is working in the field of medical psychology.