Which of the following statements are correct? (Select all that apply.)
a. Poikilotherms are often referred to as "warm-blooded."
b. Endotherms use metabolic processes to generate body heat to keep warm in cold environments.
c. Ectotherms can maintain their body temperatures because of insulation, such as blubber.
d. Shivering is a behavior used by endotherms and ectotherms to warm their bodies.