Final answer:
Deng Xiaoping's economic reforms, introducing elements of capitalism, played a major role in China's economic growth since the late 1970s.
Step-by-step explanation:
The major factor that played a major role in China's economic growth since the late 1970s was the introduction of elements of capitalism, which was implemented by Deng Xiaoping's economic reforms. These reforms included breaking up collective farms, encouraging entrepreneurship, allowing private management of state industries, and opening the country to foreign investment. The shift from a command socialist economy to a mixed economy led to significant improvements in people's incomes and the overall standard of living in China.