Used a quipu for communication--a quipu is a knot-quilt with each knot or string of knots representing a symbol or number.
Between the verbal language of the Incas and the quipu, they were able to communicate. The quipu was used to keep records and communicate information through the empire.
The topic is a matter of opinion. I feel that the drone strikes are a helpful part of the U.S. military's arsenal just as important as every other technological advancement in warfare (the gun; the automobile, such as Humvees, or even tanks; and airplanes). All these things catapulted the art of battle into the next era.
c. trade
Explanation:
I got a similar question last week