I read the book at one sitting.

我坐着一口气把书读完了。

I finished the book at one sitting.

一口气读完这本书。

He finished reading the book at one sitting.

我坐着一口气将这本书读完了。

It is an interesting book to dip into, but it cannot be read at one sitting .

这是本有趣的书，适合随意翻阅浏览，但不可能一口气读完。

He has been seized by a whim tonight and is writing several short poems at one sitting.

今晚他心血来潮，一口气写下了好几首短诗。