The most appropriate option to fill in the blank is bear.
The word bear means to tolerate or to endure. In this context, the sentence is saying that I can’t bear this pain anymore. This means that I am no longer able to tolerate the pain.
The other options are not correct.
- Bier is a type of beer. It does not make sense in this context because the sentence is not about beer.
- Boor means a rude or ill-mannered person. It does not make sense in this context because the sentence is not about a rude or ill-mannered person.
- Beer is a type of alcoholic beverage. It does not make sense in this context because the sentence is not about beer.
| 
