"i struggled with its weight; i placed it partially in its destined position. but now there came from out the niche a low laugh that erected the hairs upon my head. it was succeeded by a sad voice, which i had difficulty in recognizing as that of the noble fortunato." how does the author create surprise in these sentences? a) by withholding information b) by using flashbacks c) by revealing shocking information d) by foreshadowing

I would say the correct answer is C) by revealing shocking information. It's not that the information is withheld much - first, we suppose that the person who laughed would be Fortunato; second, this assumption is confirmed by the end of the sentence. The "low laugh" is a shocking information in itself, as it is definitely not expected in a moment when we already think that Fortunato is dead (and even if he isn't, he definitely can't have a reason to laugh).