The backbone of the teaching circle has high gold content, and the backbone of the teaching circle refers to the collective or individual who has the most fighting capacity and plays a key role in the education circle. Teaching refers to the meaning of education, and the backbone refers to the strongest and most important part. Gold content, originally the content (mass) of metallic gold in gold jewelry and gold products, is expressed by K, and the gold content per k (abbreviation of English carat and German carat, often written as K) is 4. 166%. It is often used to describe the intrinsic quality of things.