Answer: customs union.

The correct answer is **A (customs union)** because a common market represents the next level of economic integration, encompassing all features of a customs union while also allowing the free movement of factors of production among member countries. - **Option B (monetary union)** is incorrect because a monetary union involves the adoption of a common currency, which is not a requirement for a common market. - **Option C (economic union)** is incorrect because an economic union requires a higher degree of integration, including common economic institutions and coordinated policies, which go beyond the scope of a common market.

Author: LeetQuiz Editorial Team