3 Peruggia A was the guard on duty. B worked at the museum. C hid in the museum. D left his post.

Чтобы ответить на вопрос, посмотрим в текст: On that fateful Monday morning, an an called Vincenzo Peruggia was hiding in room within the museum, Peruggia, once A at the Louvre, knew the building very we guard on duty in the Salon Carré admitted his post for a few minutes at around 8 am n. Следовательно, выбираем ответ A.

Ответ: A was the guard on duty.