The correct answer is B. mortality.
Fecundity is the ability of an organism to reproduce. Mortality is the death rate of a population. Environmental resistances are the factors that limit the growth of a population, such as food, water, and predators. Biotic control is the control of a population by other organisms.
Mortality is the opposite of fecundity because it is the rate at which individuals die in a population. Fecundity is the rate at which individuals are born in a population. The two forces are in opposition because they both affect the size of a population. If fecundity is high, the population will grow. If mortality is high, the population will decline.
Environmental resistances are the factors that limit the growth of a population. These factors can include food, water, predators, and disease. Biotic control is the control of a population by other organisms. This can include predation, competition, and disease.
Both environmental resistances and biotic control can affect the mortality rate of a population. However, they are not the opposite of fecundity. They are factors that limit the growth of a population, but they do not directly affect the rate at which individuals are born.