on one's back

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释义
躺着
lying with one's back against the ground, on a bed,

例句
Phoebe:I'm so tired of being pregnant!God! I can't sleep except on my back,which hurt.(Friends)
菲比：我受够了怀孕了！天啊！我根本睡不了觉，除了平躺，还特疼。（老友记）