解释一下“fall into”释义用法，有点例句更好！

fall into

1、落入，陷入，掉进：
The boy fell into water and had to be pulled out at once.
男孩掉入了水中，必须马上拉上来。

2、盲目或无意中陷入(危险或不愉快的境地或状态)；进入(身心的某种状态，如昏迷、麻木等)；逐渐地或被动地进入(某种新的状态或关系)：
Alone in London,without friends,work,or money,Shelley fell into despair.
孤身在伦敦，没有朋友、工作和金钱，谢利陷于绝望。
After all that wine,Father fell into a deep sleep.
父亲喝了那么多酒后，就昏昏入睡了。

3、分成，分裂为；归入，属于：
These problems may fall into three classes.
这些问题可以分成三类。
This book falls into the class of children's stories.
这本书归入儿童故事这一类。

4、（河流)流入，注入：
The Yangtze River falls into the East China sea.
长江汇入东海。

5、开始(某事)；开始讨论(议题等)：
On my way home I fell into a conversation with that young girl.
在我回家的路上，我和那个年轻女士交谈了起来。

6、不知不觉地使用(某种语言)；不知不觉地做某事，毫无意识地从事某事：
Try not to fall into your native language outside class.
尽量在课外不要讲本族语言。

7、遵守，听从，服从，适应；排队，就位：
They all fell into their places.
他们各就各位。

▶BECOME◀
[intransitive, linking verb] to start to be in a new or different state
The house was empty for many years and fell into disrepair.
One false step can mean falling into debt.
He fell into despair.