Answer: C. Identifying the source of life
Explanation: The central matter of Ted Chiang's short story Exhalation is the protagonist's research about the nature of life for his metallic-based, argon-breathing alien race. New devices for breathing are mentioned, but they are secondary to the main theme and only illustrate how an unscientific, sectarian response characteristic of our mankind would happen in their world. Social interactions are mentioned when describing this alien air-centered culture. The theme of past and future is touched upon slightly when the protagonist reflects upon his discoveries.
