She sang a sad song.

她唱着悲伤的歌。

《新英汉大辞典》

I don't know your sad song.

我不知道你的难过时的歌。

youdao

What a sad song, I said, just for something to say.

多么悲伤的一首歌啊，我说，也只想说出这句话来。

youdao

When Hank sang a sad song, those who listened knew it was about something that had happened to him.

VOA: special.2009.11.22

In 1968, the group Blood, Sweat and Tears recorded this gentle, sad song about winter.

VOA: special.2009.01.26

Frank Loesser wrote this sad song, "Spring Will be a Little Late This Year."

VOA: special.2011.05.02

In between songs, Richey speaks with Melissa Block about life on tour, her late start in music and the "community" of a sad song.

NPR: At Home in Nashville with Kim Richey

LaVette sounds as if she means every word of Nelson's sad song, but the reality is that she herself has picked up the pieces of a career full of heartbreak.

NPR: Bettye LaVette Picks Up the Pieces of a Lost Career

Bridges' guileless performance makes this piquant little indie tale of country music, redemption, and the love of a pretty younger woman such a sad-song charmer.

CNN: Review: 'Crazy Heart' an indie charmer