pie in the sky 难以付诸实施的构想（或计划）;渺茫的希望;空口的许诺

【例句】
Their plans to set up their own business are just pie in the sky.
他们建立自己公司的打算只是个渺茫的希望。

The true regeneration of devastated Docklands seemed like pie in the sky.
遭毁坏码头区的真正重建看起来希望渺茫。