**Core Concept**
The demographic cycle is a model used to describe the changes in population size and structure over time. It consists of several stages, including high stationary population, early expanding population, late expanding population, and stationary population. The expanding population stage is characterized by a high birth rate and a low death rate, leading to an increase in population size.

**Why the Correct Answer is Right**
The expanding population stage is the second stage of the demographic cycle, marked by an increase in population size due to a high birth rate and a low death rate. This stage is often seen in developing countries with rapid economic growth and improvements in healthcare. The high birth rate is due to the large number of young people in the population, while the low death rate is a result of improved healthcare and living standards.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the high stationary population stage is characterized by a balance between birth and death rates, resulting in no net change in population size.
* **Option B:** This option is incorrect because the late expanding population stage is characterized by a decline in birth rate and an increase in death rate, leading to a slowing down of population growth.
* **Option C:** This option is incorrect because the stationary population stage is characterized by a balance between birth and death rates, resulting in no net change in population size.

**Clinical Pearl / High-Yield Fact**
The expanding population stage is often accompanied by a high dependency ratio, where the number of dependents (children and elderly) is high compared to the working-age population. This can put a strain on the economy and social services.

**Correct Answer:** C.