While all the options present scenarios where teamwork is explored, the choice that most directly emphasizes the theme of teamwork in a science fiction context is:
**d. by forcing characters to trust each other and work together to solve a serious problem facing humanity.**
This option highlights the necessity of collaboration and mutual trust among characters as they confront significant challenges, which is a common theme in science fiction narratives that often deal with larger existential threats or societal issues. The high stakes of a problem affecting humanity also intensify the need for teamwork, illustrating how individuals must unite their skills and perspectives to achieve a common goal.