Answer:
China's main source of economic growth are through agriculture, production of goods, transportation and cheap labour.
Each of these aforementioned factors helped in boosting the economic growth and development of China.
China's agriculture produce are exported across the globe.
It's also worth noting that China had friendly policy which attracts foreign investors through their Special Economic Zones initiated by the government.
The income generated from tax generated from the foreign investors and other IGRs were used to expand their production industry whose finished goods were transited via effective transport system such as waterways to other countries especially the USA,
All these and more made China a major commercial economy.