_______is a market where economic agents can freely exchange their endowments with each other.

The correct option is Market economy.

Explanation:

A market economy is an economic system in which decisions regarding investment, production, and distribution are guided by the price signals created by the forces of supply and demand. In such a market, individual economic agents (such as consumers and producers) own resources or endowments and have the freedom to trade and exchange them with one another based on mutual agreement and market prices.

Let's look at why the other options are incorrect:
1. Centrally planned economy: In this system, a central authority (usually the government) controls and makes all decisions regarding the production and distribution of goods and services, rather than free exchange among individual agents.
2. Aggregate demand based economy / Aggregate supply based economy: These terms refer to macroeconomic concepts and analytical frameworks rather than distinct types of market systems where agents freely exchange their individual endowments.

Therefore, a market economy is the correct term for a system where economic agents can freely exchange their endowments.