Concept:
A trade barrier is a government-imposed restriction on international trade. Governments use trade barriers such as tariffs, quotas, and regulations to control the flow of goods and services between countries.
Step 1: {\color{red}Understand the meaning of trade barriers.}
Trade barriers are measures taken by governments to regulate imports and exports. They help protect domestic industries from excessive foreign competition.
Step 2: {\color{red}Analyze the given options.}
- Promoting foreign companies is not the aim of trade barriers.
- Controlling domestic production is not their main purpose.
- Regulating foreign trade entering the country is the main objective.
- Trade barriers do not completely stop foreign trade.
Step 3: {\color{red}Identify the correct option.}
Therefore, the main purpose of trade barriers is:
\[
To regulate foreign trade into the country
\]
Hence, the correct answer is
Option (C).