Which of the following is a biotic factor that could reduce a population of frogs

a: water pollution from chemical fertillizers

b: drought that dries up ponds and puddles

c: an increase in aquatic bird population

d: a decrease in parasitic flukes

C.

Biotic mean alive, so we can cut off the first 2 easily. Aquatic birds eat frogs, so that one is safe for now. A decrease in something parasitic usually helps the population, so D is out too. The only one left is C.

your answer is going to be physical weathering