Which Southern African civilization was know for its trade and large walls? A: Kilwa

B: Nubia

C: Great Zimbabwe

D: Ancient Egypt

Great Zimbabwe

Explanation:

I hope this helps :)

c

Explanation:

answer; (quadrupled)

d. new methods of assembly are introduced.

explanation:

this allows for the goods to be made on a larger scale. not faster because now it is shown to be made better, hence the greater productivity in the question. it is calling for something new to be introduced.