What two factors often lead to a composer writing film music?

A film score is original music written specifically to accompany a film. The score forms part of the film's soundtrack, which also usually includes ... Scores are written by one or more composers, under the guidance of, or in ... schedule, a composer may have as little as two weeks or as much as three months to write the score.

Explanation:

we could tell by the rotten smell, that something putrid was in our trash can.