Natural populations fluctuate through time. One of the forces causing variation in population size is variation in the physical environment, which can have both direct and indirect effects on populations. Variation in population size linked to environmental factors (aside from those that occur daily or seasonally) is likely to:

A) be predictable and constant.
B) be density-dependent.
C) affect the biotic potential exponentially.
D) be irregular, perhaps even random.
E) track the logistic growth model.