The answer is D. Remain.
Happy Studying! ^=^
Them would be the correct pronoun for this sentence because books is plural and is an object, so its pronoun must be third person. The 3rd person plural pronoun in English is they, and its objective/accusative form (the form used when the item is the object of a verb) is them, so there's your answer.
Grammatical meaning of a word
Answer: hmm, i think they ppl should risk their safety because its the nice thing to do
Explanation: