电梯坏了，所以我们不得不爬一段楼梯。

The elevator was broken, so we had to climb ___a ___flight ___of ___stairs.

他下了一段楼梯，到达了一扇门。

He descended ___a ___flight ___of ___stairs and reached a door.

每天早上，我爬一段楼梯到我的办公室。

Every morning, I walk up ___a ___flight ___of ___stairs to my office.