The statement below is followed by four options. Each option is related to the item in the statement, but only one is always true. Select the option that always holds and makes the statement true.
"A mammal always has ______."
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A backbone
The answer must hold for every mammal, without exception. An option that is present in most cases but can be missing in even one case is not always true.
Option (1) Four legs — humans walk on two legs, and whales and dolphins have no legs at all.
Option (2) A tail — humans and apes have no tail.
Option (3) A backbone — mammals belong to the vertebrates, the animals with a backbone; every mammal has one, so this is always true.
Option (4) Ability to live on land — whales and dolphins live only in water.