What does GDP indicate about a country's economy?

The correct answer highlights that GDP, or Gross Domestic Product, specifically measures the total value of all goods and services produced within a country during a given time period. This figure is a critical indicator of economic health and performance, as it reflects the size and efficiency of an economy. A higher GDP generally suggests a growing economy, indicating that businesses are producing more goods and services, which typically correlates with higher employment rates and increased consumer spending.

In contrast, while factors such as the quality of life and happiness may be influenced by economic performance, GDP does not directly measure these aspects. Similarly, the number of businesses operating within the economy can be indicative of economic activity but does not capture the overall value generated. Finally, foreign investment levels can provide insights into economic attractiveness and confidence but, again, are not encompassed in the GDP figure itself. Thus, GDP serves as a clear and focused measure of a country's economic output, making it the best answer in this context.