To create a stable population, the population change should be zero, which means that Natality (births) should equal Mortality (deaths) plus Immigration (people moving in) should equal Emigration (people moving out).
This can be expressed with the equation: \[ \text{Natality} - \text{Mortality} + \text{Immigration} - \text{Emigration} = 0 \]
Rearranging this to relate natality, mortality, immigration, and emigration gives us:
\[ \text{Natality} + \text{Immigration} = \text{Mortality} + \text{Emigration} \]
Therefore, the correct choice among the responses provided is:
natality + immigration = mortality + emigration