Final Answer:
Bitter would be a caustic response to a hostile question. Therefore, the correct option is a).
Step-by-step explanation:
In the given context, a "CAUSTIC" response to a hostile question implies a harsh and critical reply. The term "caustic" is associated with a sharp, biting, and sarcastic tone that is intended to express disapproval or disdain. Therefore, the synonym for a caustic response in this scenario is "bitter," capturing the essence of a sharply critical and hostile reply.
A caustic response often involves the use of cutting remarks or harsh language to counteract hostility. It is characterized by its acerbic and corrosive nature, aiming to sting or wound emotionally. While other options such as "kind," "mild," or "soothing" represent responses with a more gentle and positive tone, "bitter" aligns with the idea of a caustic retort that reflects a confrontational and unfriendly attitude.
In summary, the synonym "bitter" best captures the nature of a caustic response, emphasizing its sharp and critical character in the face of a hostile question.