There would be no separation between one country's economy and another's if the entire world:

• A. maintained strict immigration controls
• B. had different governments but similar cultures
• C. imposed tariffs on all imported goods
• D. used a single currency and had completely free trade

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the concept of economic integration and what it means for countries' economies to be separated or unified. Economic separation typically arises from barriers such as tariffs, different currencies, immigration controls, and distinct government policies.
2. Step 2: Analyze the impact of strict immigration controls. These controls limit the movement of labor between countries, maintaining economic separation despite other factors.
3. Step 3: Consider the effect of having different governments but similar cultures. Different governments can still enforce different economic policies, which can keep economies separate even if cultures are alike.
4. Step 4: Evaluate the role of tariffs on imported goods. Tariffs act as trade barriers, restricting the free flow of goods and services, thus maintaining economic separation.
5. Step 5: Recognize that using a single currency and having completely free trade removes major barriers to economic integration. A single currency eliminates exchange rate risks and transaction costs, while free trade removes tariffs and quotas, effectively uniting economies into one large market without separation.