Answer: The correct answer is A: BCC your supervisor in your response.
Explanation: BCC stands for Blind Carbon Copy, and it is a feature that allows you to send an email to multiple recipients without revealing their addresses to one another. If you want to discreetly notify your supervisor about the unpleasant email from your coworker, you can use the BCC feature to send a copy of your response to your supervisor without your coworker knowing. This will allow you to bring the issue to your supervisor's attention without involving the coworker or creating any unnecessary conflict.
Option C, Reply All and add your supervisor in the To field, would also work, but it would reveal your supervisor's address to the coworker. Option D, Reply and add your supervisor in the To field, would only send a copy of the original email to your supervisor, rather than your response to it. Option B, CC your supervisor in your response, would also reveal your supervisor's address to the coworker and would not be a discreet way to notify your supervisor.
