It's Plum Blossoms Sweeping Wax Snow, which is taken from Feng Zikai's Story of Juvenile Music and Art, an article explaining the knowledge of scales.

The Story of Juvenile Music and Art is a series of stories of artistic enlightenment created by Feng Zikai as his father. As protagonists, the two brothers and sisters tell their first study of art and music in this book, and the basic knowledge of art and music runs through it. For example, perspective in art, chromatics, basic music theory in music, commonly used musical instruments and so on.