The answer is a. hope that helped :)
I also agree that the answer is B: whom
in this sentence you are using the preposition + whom grammar structure. Whom is considered an object pronoun and is used when asking who will receive the action, which in this case, I believe is, baking those cookies. Hopefully this makes sense and good luck.
Answer:
You should be asking 2 things, how can I use it in my own writing and what is the meaning and effect of this technique
