Which of the following statements about trophic cascades is TRUE?
a. A trophic cascade occurs when predation limits herbivore abundance and plant population sizes are reduced
b. A trophic cascade occurs when a predator is removed, allowing plants to expand, which then limits herbivores
c. In a trophic cascadel plant abundance depends on the number of trophic levels in the community
d. A behavioral cascade Which often involves the perception of predation risk is not a type of trophic cascade.