- Non-mammals do not nurse their offspring
- A mammal usually nurses its offspring
- Hence, only mammals nurse their offspring

- Glands that make milk are only used for making milk
- Milk is generally only used for nursing offspring
- Therefore, glands that make milk are only useful for nursing offspring

- Only mammals nurse their offspring
- Glands that make milk are only useful for nursing offspring
- Therefore, glands that make milk are parts of only a mammal

Therefore, glands that make milk are parts of only a mammal
[Question]Which characteristic is found ONLY in mammals?
[Context]- Glands that make milk are only used for making milk 
- Milk is generally only used for nursing offspring 
- Non-mammals do not nurse their offspring 
- A mammal usually nurses its offspring