GRE Sample Test 2 Verbal Reasoning 2

The word that fills the blank must describe “the stench of the livestock,” which is so malodorous that it drives the newcomers back to the city; it must mean something like, well, “stinky.” Both noisome and mephitic are appropriate choices.
The other words don’t work; if you were tempted by olfactory, realize that it simply means “related to the sense of smell” and does not actually describe a particular scent.