The answer is B) Inca. Extensive road network across plains, deserts and mountains reaching all corners of the empire was one of the notable features of the Inca empire like terraced farming, canals, crop rotation and irrigation as agricultural innovations. It allowed smooth military operations, trading, and the use of runners or chasquis.
Density (a) is the correct answer
<span>Scientists believe that differences in density cause hot, plastic-like rock in the asthenosphere to rise toward earth's surface. </span>
