"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
Engineers and scientists are slightly different, with engineers focusing more on the application of science. They are often seen as the link from scientific discoveries to their application in the real world.