The correct answer is - stationary.
The stationary population pyramid is a pyramid where the changes in the population are minimal, the death rates are high and at a younger age, while the birth rates are also high.
Because there are high birth rates, but also high death rates, the population remains almost unchanged. The majority of the population is very young, with the middle aged people being the second in numbers, and the elderly people are almost non-existent because of the very low life expectancy.
This type of population pyramid is typical for the least developed countries in the present, but was also the dominant population pyramid for most of the human history.