Answer:
As if merely subsisting according to his self-imposed rules weren’t strenuous enough…
Step-by-step explanation:
The word "subsist" is a gerund that means sustenance, dependent, survival on one's own. In other words, it means the ability or capacity to support and survive by oneself on a minimal level.
The given line "as if merely subsisting according to his self-imposed rules weren't strenuous enough..." is from Jon Krakauer's "Into the Wild." The lines go like this-
As if merely subsisting according to his self-imposed rules weren't strenuous enough, Rosellini also exercised compulsively whenever he wasn't occupied with foraging. He filled his days with calisthenics, weight lifting, and running, often with a load of rocks on his back. During one apparently typical summer, he reported covering an average of eighteen miles daily.
Thus, the correct word for the blank in the line is "subsisting".