Samuel Ullman once said:" Youth is not a time of life , it is a stage in mind ; it is not a matter of rosy cheeks , red lips and supple knees; it is a matter of the will , a quality of imagination, a vigor of the emotions;it is the freshness of the deep springs of life."

vigor n.活力
supple adj. 柔软的
lip n.嘴唇
freshness n. 新鲜