They can distinguish a happy tune from a sad one.

他们能分辨出曲调是快乐还是悲伤的。

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The boy whistled a happy tune.

那孩子用口哨吹奏愉快的曲调。

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The flute player piped a happy tune.

那个吹笛子的人吹奏了一支欢快的曲子。

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As for me, I'll just shuffle off to my cabin in the sky and whistle a happy tune as I make up my own list.

NPR: The Greatest Musicals? 'Singin' in the Rain' Tops List

Do you skip to the office every morning, whistling a happy tune, with an eager sense of anticipation about what the day might have in store?

BBC: Wales Office: you don't have to be sad to work here..

Adorno meant that the magnitude of modern-day evil made the old-fashioned pursuit of aesthetic consolation, via poetry, music or whatever, the spiritual equivalent of plugging one's ears and humming a happy tune: immature, cowardly, even immoral.

WSJ: Henryk G��recki | Symphony of Sorrowful Songs | A Lament for Lost Children | Masterpiece by Ian Marcus Corbin