"Zach is using psychological principles and research methods to determine methods for athletes to reach their peak performance, while Anna is utilizing psychological principles in developing ways to alleviate traffic jams in growing cities. Both of these psychologists are working in the field known as psychology."

a. basic research
b. forensic
c. comparative
d. applied

Applied psychology

Explanation:

Zach and Anna both working in applied psychology as Applied psychology refer to imply all theoretical and principal knowledge to solve everyday problem of human and animal behavior. Simply use all strategist and techniques, theories in experiment. research to conduct ad observe practical  psychology of human and animal experience.

Both of these Psychologist are working in the field known as APPLIED PSYCHOLOGY.

Explanation: Applied Psychology can be defined as the putting into practical use the principles of Psychology.

Applied psychology involves putting practical research into action. Just like Zach and Anna in the question, they Implement practical research methods to real life situations like improving performance for athletes and alleviating traffic jams in cities respectively.