They have finished to do exercise; they are -_ right now

Lucy lined up the old postcards in the order they had arrived, placing each one carefully so that the edges of all the cards touched, but didn't overlap. she sipped her tea, remembering the day each card had arrived, when she'd hurried to the end of the driveway and opened the mailbox, picking through the blackberry bushes that grew wild on either side of it, to find a thin card lying inside like a treasure. in the passage, what is the best example of an artifact? a. the treasure b. the postcards c. the mailbox d. the tea