Step 1: Analyze the passage's core message.
The passage describes a pattern where each generation criticizes the succeeding one, disregarding their own past experiences of youth. Adults often dismiss their youthful mistakes while condemning similar behaviors in current young people, highlighting a discrepancy in their judgment.
Step 2: Fill in the conceptual gaps.
- The first blank requires a term indicating one generation following another, so “successive generation” is appropriate. - The second blank refers to the state that is forgotten, which is being “young.” - The third blank identifies the group reflecting on their past, which is the “adults.” - The fourth blank describes the manner of their condemnation, which is “hypocritically,” due to their past actions.
Step 3: Discard incorrect options.
- (A) “cautiously” does not align with the passage's critical tone. - (B) Using “young” twice would be redundant and stylistically poor. - (D) “naturally” fails to convey the element of hypocrisy. - (E) “sincerely” contradicts the observed double standard. Therefore, Option C is the most suitable choice.
Final Answer: \[\boxed{\text{C}}\]