Which Statement About the Studies by Mary Power and Colleagues

Which statement about the studies by Mary Power and colleagues on California rivers is true?

A) In drought years the number of trophic levels increased.
B) Species, such as the steelhead, that are keystone predators during normal years are minor players in the food web during drought years.
C) The alga Cladophora completely died out during droughts.
D) Species interactions remained constant despite changes in environmental conditions.