Cetaceans reduce the number of breaths they take during rest periods.鲸类动物在休息时减少它们的呼吸次数.It is not clear whether cetaceans undergo dream sleep.鲸类动物是否经历梦睡眠还不清楚.Missing until recently were fossils clearly intermediate, or tr...

cetaceans的音标：...

n.鲸目动物( cetacean的名词复数 )...