Fact 1: Mammals generate heat mainly by keeping their metabolic rate high.

Fact 2: Birds have a high metabolic rate and a high energy requirement.

Given the two facts above, answer the question "What mammals have a high energy requirement and generate heat?" with the following options: 
- cats
 - bats
 - Crustaceans
 - bears
 - frogs
 - lizards
 - birds
 - mammals


 

       birds  