B) The second sentence implies that the night watchman is stressed and underfed; the first implies that he is gracefully lean.
Explanation:
While the adjective "slender" makes reference to the man's physique, meaning that he has a healthy weight and the characteristics of a slim person, the adjective "gaunt" refers to the deplorable conditions in which the man is. By being "gaunt", he looks malnourished and is probably in an inadecuate pysichological condition.
He pride's himself as a wine taster and Montessor uses this against him. Additionally when they head into the catacombs Fortunato refuses to back out even he is dizzy and is drunk.
