The pattern is formed by adding 1 and then adding 9 alternately. So, the rule that best describes the pattern is: A. Add 1, add 9, repeat.
The pattern 5, 6, 15, 16, 25, 26, 35, ... follows the rule of alternately adding 1 and 9. Initially, 1 is added to 5, then 9 is added to 6, and this alternating sequence continues. This pattern is accurately described by the rule "Add 1, add 9, repeat," making option A the correct choice.
Recognizing such patterns is fundamental in mathematical reasoning and problem-solving, emphasizing the significance of identifying regularities within sequences. In this case, the consistent alternation of the two specified values forms the basis of the progression, enabling a concise and logical rule to characterize the entire sequence.