External contact and intercultural exchange benefitted early civilizations. This is true of both the civilizations of sub-Saharan Africa and those of Southeast Asia.
In the case of Sub-Saharan Africa, one such civilization was that of the Kingdom of Kush. This was established around 1070 BCE. Kush developed in a region known as Nubia, in the Sudanese and southern Egyptian Nile Valley. Much of the success of the Kingdom of Kush came from its interactions with Egypt. Kush was an important producer of gold and ivory, and by trading with Egypt, it achieved great wealth. It also acquired some of the traditions of Egypt, such as the building of pyramids and mummification.
Southeast Asian civilizations also benefitted from trade in their early years, particularly maritime trade. The Austronesian people built the first ocean-going ships. They trade with areas such as Southern India and Sri Lanka. This also connected these people with the cultures of India and China. This trade led to a rise in technological knowledge and traditions. Some of the items that were exchanged in this trade were catamarans, outrigger boats, sewn-plank boats, coconuts, sandalwood, bananas, and sugarcane.
B is the Answer. The Yangtze
I think that a) is chemical, and b) would be chemical
