Class 'Mammalia' includes (a) Fish (b) Frogs (c) Birds (d) Humans

First, recall the characteristics of mammals. Mammals are warm-blooded vertebrates characterized by having hair or fur, mammary glands in females, and usually giving birth to live young.

Assess each option to determine if it shares the characteristics of mammals. (a) Fish: Fish are cold-blooded and do not have fur or mammary glands. Therefore, fish do not belong to the Class Mammalia. (b) Frogs: Frogs are amphibians, which means they are cold-blooded and do not have hair or mammary glands. Therefore, frogs do not belong to the Class Mammalia. (c) Birds: Birds are warm-blooded and have a few similarities with mammals, but they have feathers instead of hair or fur and do not have mammary glands. Therefore, birds do not belong to the Class Mammalia. (d) Humans: Humans are warm-blooded, have hair, and females have mammary glands. Additionally, humans give birth to live young. Therefore, humans belong to the Class Mammalia.

The correct answer is (d) Humans, as they best represent the characteristics of the Class Mammalia.