Final answer:
In most contexts, 'demanding' and 'rigid' are the words most similar in meaning to 'rigorous', as they imply a level of strictness and exactness.
Step-by-step explanation:
The word rigorous typically means something that is extremely thorough, exhaustive, or accurate. It often carries a connotation of strictness and precision in execution or practice. In the context of most passages, the words demanding and rigid would be the closest in meaning to rigorous, as they both imply a level of stringency and inflexibility. 'Demanding' suggests that something requires a lot of effort, dedication, or adherence to strict standards. 'Rigid' means that something is unwavering or fixed in its rules or standards. Although 'harsh' and 'severe' can sometimes be used similarly, they are more often associated with punishing or extreme hardships rather than thoroughness and precision.