If a city suddenly shows population growth and birth rate has not changed, which cause should be checked first?

Correct answer: Immigration or a change in administrative boundaries

The direct answer is B: check immigration or a change in the administrative boundary. Population change is not produced by births alone. If the birth rate has stayed unchanged, a sudden increase may result from people moving into the city. It may also appear when nearby settlements are included because the city boundary has been expanded or redrawn. A is not the best first explanation because rainfall does not directly account for a sudden counted increase in population. C is unrelated to the demographic calculation. D is wrong because the death rate must be measured or estimated, not simply assumed to be zero. A boundary change can alter the recorded population even when the actual number of residents has not suddenly changed. Memory cue: for a sudden increase, check migration and measurement boundaries before assuming a sudden fertility change.