WBCS Preliminary Examination 2023 — General Studies · Question 18 of 200

Answer: (D) Stream

PSC's key gives "Stream". A pond and a lake are both standing (lentic) water bodies, and "water body" is the general term that covers them, whereas a stream is running (lotic) water, which makes it the odd one out. An alternative line of reasoning is that "water body" is the genus and the other three are its species, but the PSC did not accept that reading. Remember the ecology terms: lentic ecosystems are still waters (ponds, lakes, wetlands) and lotic ecosystems are flowing waters (streams, rivers).