有一天，我回到家发现窗户碎了。

___One ___day, I came home to find my windows broken.

有一天，我正在读一本有趣的书，这时有人给我打电话。

___One ___day, I was reading an interesting book when someone called me.

有一天，我的狗学会了如何开门。

___One ___day, my dog learned how to open the door.