The relationship between the values of a country’s imports and its exports is called.

The correct option is Balance of Trade.

Explanation:
The relationship between the value of a country's imports and its exports is defined as the Balance of Trade (BOT). It represents the net flow of physical goods (visible trade) between a nation and the rest of the world over a specific period of time.

The formula representing this relationship is:

$$\mathrm{Balance\; of\; Trade}=\mathrm{Value\; of\; Exports}-\mathrm{Value\; of\; Imports}$$

Depending on the values, the Balance of Trade can be categorized as follows:
1. Trade Surplus: Occurs when the value of a country's exports is greater than the value of its imports.
2. Trade Deficit: Occurs when the value of a country's imports is greater than the value of its exports.
3. Balanced Trade: Occurs when the value of exports exactly equals the value of imports.

Why the other options are incorrect:
- Balance of Payment (BOP): This is a broader term that records all economic transactions (including services, capital, and financial transfers, in addition to goods) between residents of a country and the rest of the world.
- Balance of currency: This is not a standard financial or economic term for the import-export relationship.
- Bill of exchange: This is a written, unconditional order used in international trade that binds one party to pay a fixed sum of money to another party at a future date.