In a country, at any time, the population has the same number of youngs and mature ones. What type of growth does it reflect?

The correct option is Stable.

In population ecology, the growth status and future trend of a population can be understood by analyzing its age structure, which is typically categorized into three ecological age groups: pre-reproductive (young), reproductive (mature), and post-reproductive (old).

When the population has an equal number of individuals in the young (pre-reproductive) and mature (reproductive) age groups, the rate of replacement is exactly equal to the rate of transition into the mature class. This indicates that the population is neither expanding (which requires a very high proportion of young individuals) nor declining (which is characterized by fewer young individuals compared to mature ones). Instead, the birth rate is balanced with the growth and replacement rates, leading to a stable population size over time. Therefore, this age distribution reflects a stable type of growth.