Answer;
The similarity between gills and lungs is that both are sites for gaseous exchange in living organisms.
Explanation;
Gills is a site for gaseous exchange in fishes amphibians at some stage in life; while the lungs is a site of gaseous exchange in mammals and other organisms such as reptiles.
They both serve to bring in oxygen in the living things body and the eliminate carbon dioxide from the body; process of gaseous exchange.
However, they differ in a number of ways; for example, lungs are internal while gills are external , lungs are developed to breath in oxygen from the air, while gills are developed to get oxygen from water.