If it has been revised, but the answer has not been saved, it is equivalent to a white change.

Minghua Online is the official website of the massive open online course alliance of domestic high-level universities. The Alliance is an open cooperative education platform voluntarily established by some high-level universities in China. It is a public welfare, open, unofficial and unincorporated cooperative organization. The aim is to build a high-level large-scale online open course platform with China characteristics through exchanges, discussions, consultation and cooperation, and provide members and society with a large number of high-quality open online courses.