The correct answer is option 'C' - Neolithic age.

In order to understand why the heeled cart was made in the Neolithic age, let's first understand what the Neolithic age was and the advancements that took place during that time.

Neolithic Age:
The Neolithic Age, also known as the New Stone Age, was a period of human history that started around 10,000 BCE and lasted until around 4,500 BCE. It was characterized by the transition from hunting and gathering to settled farming communities. During this period, humans began to domesticate animals, cultivate crops, and develop more advanced tools and technologies.

Advancements in the Neolithic Age:
1. Agriculture: One of the major advancements in the Neolithic age was the development of agriculture. Humans started to cultivate crops such as wheat, barley, and legumes, which led to a more settled lifestyle as they no longer had to rely solely on hunting and gathering for food.

2. Domestication of animals: Along with agriculture, humans also began to domesticate animals. They started keeping animals like cattle, sheep, and goats for milk, meat, and labor. This allowed them to have a stable source of food and other resources.

3. Pottery: The Neolithic age saw the emergence of pottery as a significant technological advancement. Pottery vessels were used for storing food, water, and other items. The invention of pottery allowed for better preservation of food and the development of more complex cooking techniques.

4. Tools and Weapons: The Neolithic age witnessed the development of more sophisticated tools and weapons. Stone tools such as axes, knives, and scrapers were improved upon, and new materials like polished stone and flint were used to make them more efficient.

5. Transportation: The invention of the wheel revolutionized transportation during this period. The wheel was initially used for making pottery but soon became an important means of transportation. The heeled cart, which had a fixed axle and wheels with a solid rim, was developed during the Neolithic age. It allowed for the transportation of heavy goods and materials over longer distances, making trade and communication easier.

Conclusion:
The heeled cart was made during the Neolithic age because this period saw significant advancements in agriculture, domestication of animals, pottery, and tool-making. The invention of the wheel and the development of the heeled cart played a crucial role in improving transportation and facilitating trade and communication among different settlements.