Environmental resistance causes populations to decline. Option B is correct
Environmental resistance refers to the sum of all factors in an environment that limit the growth of a population. These factors can be biotic (e.g., competition, predation) or abiotic such as lack of resources, extreme temperatures. When environmental resistance is high, it becomes more difficult for a population to survive and reproduce, causing it to decline in size.
While some populations might achieve temporary stability at certain levels of environmental resistance, the overall tendency under this pressure is for the population size to decrease.