Task: Question Answering
Input (English): Passage: In 1988, when Katrina "Kat" Connors was 17, her beautiful but mercurial mother, Eve, disappeared without a trace. The story weaves back-and-forth with flashbacks of Eve's past life and the present day.
In the flashbacks, Eve was a wild girl who gradually changed into a domesticated housewife after marrying Brock, an ordinary man who leads an uneventful life. While Kat explores her blossoming sexuality with her handsome but dim-witted neighbor and schoolmate, Phil, Eve struggles to deal with aging and quenching her youthful wildness. She tries to be sexy when Brock is away, even luring Phil's attention. After Eve disappears, Kat deals with her abandonment without much issue, occasionally releasing her own wild side, seducing the detective investigating her mother's disappearance. The film then jumps forward three years to the spring of 1991. On a break from college, Kat returns home and seems unfazed to learn that her father is in a relationship with a co-worker.
The detective Kat has been having an affair with informs her that Brock might have killed Eve after catching her cheating. Kat dismisses this theory, just like she did three years ago, but after mentioning the topic to her friends Beth and Mickey they tell her they suggested this same theory to her and she dismissed them as well. Kat suspects Phil of having slept with Eve and confronts him the night before she is to return to college, but Phil angrily rebuffs it and tells her that her father knows where her mother is. 
Question: What time of year is it when Kat learns about her dad's new relationship?
Output (English): spring.