It ruins a book to double back the pages as a bookmark.

把书页折起来当作书签用会把书弄坏的。

The road ahead is flooded so we have to double back.

前面的路已遭水淹，我们只好原路折回。

If you double back the blanket, it will be more comfortable.

如果把毯子叠起来会更舒服。

As it grows outward, it runs out of room and is forced to double back into a horseshoe shape.

随着它向外生长，空间扩大，增大为以前的两倍，成了马鞋的形状。

The roads leading to the most beautiful places always twist and turn and double back on themselves.

通往最美丽的地方的路总是曲曲折折而且有时候不得不返回起点。