It is such a common rectangular blackboard, but it is the golden key to the door of the treasure house of knowledge.

就这样一个普通的长方形黑板，可却是通往知识宝库的金钥匙。

youdao

It is such a common rectangular blackboard, but it is the golden key to the door of the treasure house of knowledge.

就这样一个普通的长方形黑板，可却是通往知识宝库的金钥匙。

youdao