Birds and mammals share one of the following characteristics as a common feature.
(a) Pigmented skin
(b) Pneumatic bones
(c) Viviparity
(d) Warm blooded
Ans. (d) Warm blooded
Explanation: Pneumatic bones and viviparity is present in birds but not in mammals. Pigmented skin is present only in mammals. Hence, ‘d’ is the correct option.
