Final answer:
Sentence 3 stands out as evidence within the paragraph about the importance of zoos in protecting animals, particularly highlighting the successful breeding of Sumatran tigers at the National Zoo.
Step-by-step explanation:
The sentence that is part of the evidence in the paragraph about zoos being needed to protect animals is Sentence 3. This sentence provides a specific example of how a zoo has contributed to conservation efforts by breeding a critically endangered species, the Sumatran tiger, and thus supporting the population which was once only seven hundred in the world. Such evidence supports the claim that zoos play a crucial role in saving endangered species and bolstering their numbers through captive breeding programs and conservation efforts.