Which of the following best illustrates a common market?

A common market is an integration agreement among countries that allows for the free movement of goods, services, capital, and labor, similar to a single market but with some additional features. The essence of a common market is the removal of trade barriers, and more importantly, the freedom of movement for labor across borders. This characteristic enables workers from member countries to seek employment in other member countries without restrictions, promoting economic flexibility and labor allocation according to demand.

This concept is reflected in the choice that highlights the free movement of labor. It underscores how citizens of member nations can work in any of the partnering countries, thus maximizing their employment opportunities and enhancing the labor resource pool for businesses.

In contrast, the other choices highlight elements that may exist in various markets but do not independently define a common market. A market with no tariffs or quotas could represent a free trade area, while a single currency pertains more to a monetary union rather than all the freedoms associated with a common market. Strict immigration policies would contradict the very principle of a common market, which emphasizes openness and fluidity among member nations' workforces.