Final answer:
A common market is an economic agreement that allows for the free trade of goods, services, labor, and capital among member countries, while also pursuing a common external trade policy.
Step-by-step explanation:
A common market is an economic agreement between countries that allows for the free trade of goods, services, labor, and financial capital among its members. Additionally, it involves the pursuit of a common external trade policy. This means that the member countries agree to have a unified approach to trade with non-member countries. Therefore, the correct answer to the question is d) Only b and c.