The true statement about economic systems is A. Ancient humans engaged in early economics by trading and selling goods.
Early economic systems can be traced back to ancient civilizations where individuals engaged in trading and selling goods as a means of obtaining resources they needed. For example, ancient civilizations such as Mesopotamia, Egypt, and China had established trade networks and markets where people exchanged goods and services. This early form of economics played a crucial role in the development of societies and laid the foundation for more complex economic systems that emerged later.