1. I was disappointed at the movie's ending.

2. I was disappointed with the movie's ending.

3. I was disappointed in the movie's ending.

4. I was disappointed by the movie's ending.

(They are passive voice sentences. Which one is right? Which preposition do we have to use?)

All are correct, and all are used by just about everyone. It's a strange one! It doesn't seem to matter which preposition you use, in this case!!

All four sentences are grammatically correct, but they have slightly different nuances. The choice of preposition depends on the context and the intended meaning. Let's break it down:

1. "I was disappointed at the movie's ending."
In this sentence, "at" is used to indicate the specific point or event at which the disappointment occurred. It suggests that the ending itself was the cause of disappointment.

2. "I was disappointed with the movie's ending."
Here, "with" is used to show that you were disappointed overall with the movie, and the ending was one aspect that contributed to that disappointment. It implies that the ending was not the only factor, but it played a role in your negative perception of the movie.

3. "I was disappointed in the movie's ending."
Using "in" expresses disappointment in the quality or execution of the ending itself. It suggests that you found the ending unsatisfactory or that it did not meet your expectations.

4. "I was disappointed by the movie's ending."
Using "by" indicates that the ending was the direct cause of your disappointment. It implies that the ending had a negative impact on your overall experience of the movie.

In summary, the choice of preposition depends on the specific meaning you want to convey. If you want to emphasize the ending as the cause of disappointment, "at" or "by" may be more fitting. If you want to convey a broader sense of disappointment with the movie as a whole, "with" or "in" might be more appropriate.