Astrid was emotionally aroused by a tv horror movie. she became extremely angry when her younger brother momentarily blocked her view of the screen. when her movie viewing was interrupted by a phone call from her boyfriend, however, she experienced unusually intense romantic feelings. astrid's different emotional reactions to her brother and her boyfriend are best explained by the

The difference in emotional reaction could be explained by Schachter two-factor theory; labeling emotion to the event
When Astrid is watching the horror movie, the emotional arousal would induce the production of adrenaline within her body, which create a sense of excitement.
When the boyfriend called under this circumstances, she will associate that sense of excitement toward the existence of the boyfriend that could be interpreted as love.