问答题 Birds evolved during the great reptilian radiation of the Mesozoic era, Amniotic eggs and scales on the legs are just two of the reptilian features we see in birds.But modem birds look quite different from modem reptiles because of their feathers and other distinctive flight equipment.
【正确答案】metabolic heat
【答案解析】文章第三段第二句提到,鸟类利用自身代谢的热量来保持温暖和恒定的体温。因此,填入metabolic heat。