THREE:In studying improvements with a view to practical gain, a learner can have no reasonable hope of accomplishing much in fields already gone over by able engineers, nor in demonstrating anything new in what may be called exhausted subjects, such as steam-engines or water-wheels; he should rather choose new and special subjects, but avoid schemes not in some degree confirmed by existing practice.
宝宝健康饮食是成长的关键,为了满足其生长发育所需要的各种营养,就必须对日常饮食做出合理安排。黄瓜和胡萝卜中含有丰富营养素,让宝宝吃得健康!