This is( )song I've told you about.Isn't it ( ) beautiful one?the,the?a,a,the?the,

This is( )song I've told you about.Isn't it ( ) beautiful one?the,the?a,a,the?the,
This is( )song I've told you about.Isn't it ( ) beautiful one?
the,the?a,a,the?the,

This is( )song I've told you about.Isn't it ( ) beautiful one?the,the?a,a,the?the,
song后面有定语修饰,所以要特指 ,用the
否定疑问句不用特指,用a

the ,a

the, a
这是我给你提过的那首歌。（定指， 用the）
是一首优美的歌曲吧？（不定指，用a）

THE song后面有从句来修饰,特指told you的那首歌,所以用the.
A 没有特指, 用a就对了.