B. principal-agent problem.
Traders working for banks are subject to the principal-agent problem, which refers to the conflict of interest that arises when one person or group (the principal) hires another person or group (the agent) to act on their behalf. In this case, the bank is the principal and the trader is the agent. The principal-agent problem arises when the agent has incentives that are misaligned with those of the principal, leading to potentially harmful behavior by the agent.