Step 1: Understand each clue.
The given clues are: Deer, Tiger, Kangaroo, Hippopotamus. These are four different animals from different habitats and characteristics, so we must identify a feature or classification that connects all of them.
Step 2: Evaluate each option.
(A) Pouch: Only kangaroos have pouches; others do not. So this cannot be the correct answer.
(B) Stripes: Only tigers have stripes; other animals listed are not striped. Hence this does not fit all clues.
(C) Mammals: All four — deer, tiger, kangaroo, and hippopotamus — belong to the category of mammals. This matches every clue perfectly.
(D) Zoo: Although these animals may be found in zoos, the connection is too broad and not unique.
(E) Australia: Only kangaroo is native to Australia; others are not related to it.
Step 3: Conclusion.
Since all four animals are mammals, the only alternative that is associated with every clue is option (C) Mammals.