As an old man, he is ambitious for a thousand miles; as a martyr in his old age, his ambition is endless.——Cao Cao.
It is the time for men to study when the lights are on at three o'clock and the chickens are on the fifth o'clock. Black-haired people don't know how to study early, and white-haired people regret that they are late in studying. - Yan Zhenqing
Animal taxonomists are based on the characteristics of animals. Various characteristics (morphology, cells, genetics, physiology, ecology and geographical distribution, etc.) are classified, and animals are divided into six main levels, namely phylum, class, order, family, genus, and species.