What is the theme sentence of this song?

Music theme is the most important idea in a piece of music (paragraph), that is, the core of music.

It is the "seed" of musical thinking, which mostly appears in the form of melodies with strong singing, and has the characteristics of distinctive personality, strong expressive force and relatively complete summary of sound and meaning. Excellent music themes all contain rich ideological connotations. The word theme has the meaning of topic, composition and discussion. Italian music theorist Zollino first used it in music in16th century. He refers to the melody that appears repeatedly in his works and is associated with variation. Later, in fugue and tonic music, the theme is often indicated as the beginning of the whole song.

The general rule is that the theme of music appears at the beginning (or after the introduction) of music. In miniature music works, the main body is often the music itself, such as the traditional folk song "Blue Flower" in northern Shaanxi. In small-scale works, there is generally only one theme, and it consists of more than two phrases, such as "Without the production party, there would be no new China" (lyrics by Cao Mars). There are many other situations. In large and medium-sized works, there are two or more themes, which represent different musical figures and cause contrast, and most of them appear in the form of paragraphs. For example, the violin concerto Butterfly Lovers (He and Chen Gangqu) consists of a main theme and a sub-theme; In the fourth movement of Beethoven's Ninth Symphony, there are sixteen "Ode to Joy" themes.