Answer:
B) By whom were those pictures taken?
Step-by-step explanation:
“Whom” is a pronoun that refers to the object of a verb or a preposition (like “by,” “to” and “from”), meaning that this pronoun does not replace nouns performing the main action, but, instead, it replaces those receiving the main action. Sentence B, then, is using this pronoun correctly because in here it is acting as the object of the preposition “by.”