The film was quite boring -> we....the film     (bored)

The correct completion of the sentence is "We were bored by the film."

In this context, "bored" is the past participle form of the verb "bore," which means to cause someone to feel uninterested or tired. When you say "We were bored by the film," it indicates that the experience of watching the film resulted in feelings of boredom.

The structure "were bored" is used in passive voice, where "were" is the auxiliary verb that helps to indicate the past tense, and "bored" describes the state of the subject (us) as a result of the film. Therefore, it captures the idea that the viewers found the film uninteresting or dull.

In contrast, if you were to say "We bored the film," it would imply that "we" caused the film to be uninteresting, which doesn't fit the intended meaning. Thus, the appropriate sentence structure reflects the experience of the viewers in relation to the film.