Answer:
The correct answer would be option B, Rachel spend all morning writing a difficult report, but she believes that willpower is an unlimited resource and that she thus has a lot of it.
Explanation:
Rachel wanted to laugh hard on the outfit which her boss was wearing in the office. According to her, that was the most silliest outfit she has ever seen. But she controlled herself from laughing. The best way to control herself was to make herself busy in a task which is tough enough that she doesn't find time to think about the boss's outfit. Secondly she also believes that willpower is the main resource which a person can has and she has a lot of it, so she is able to control her behavior through her willpower.