Pie in the sky 天方夜谭

It mean something unrealistic, not practical

When first invented, the car and phone were pie-in-the-sky ideas. Now we have phones in cars.

pie in the sky的意思是不切实际的东西.

汽车和电话在被发明出来以前都是天方夜谭，但是现在我们在汽车中打电话