Exercise:

1. What genre has this feature: alternative timeline.

Sci-Fi.

2. What genre has these features: fast pace and tension.

Thriller.

3. What genre has this feature: multiple suspects.

Mystery.

4. When your work features more than one genre, how do you narrow it down to one?

You focus on the main theme of your story. For example, in "Romeo and Juliet," there is love, violence, backstabbing, and death. One might think to classify Shakespeare's work as romance, but it's core theme is tragedy.