Which can be a direct cause of population increase in an area?

Correct answer: Increase in the number of births

The direct answer is A: an increase in the number of births can directly increase population. Each birth adds a new person to the population of the area, so more births mean more additions, all else being equal. B is wrong because an increase in deaths removes people and tends to reduce population. C is wrong because out-migration means people leave the area, which also lowers its population. D is wrong because a lower birth rate means fewer births relative to the population, so it does not directly produce an increase. Population change can also be affected by in-migration and out-migration, but among the given choices, increased births are the clear direct cause. Remember the balance: births and in-migration add people; deaths and out-migration remove people. The wording “can” is suitable because other processes may influence the final total.