I realize we don't have a full explanation for this tricky Necessary Assumption question, so here goes!
The core of this argument is:
Premise: 65+ people continue working --> young people unable to get jobs they trained for --> dissatisfaction
+
Premise: Unfair for workers of 40+ years to block opportunities for others
LEADS TO
Intermediate Conclusion: 65+ are permitted to continue working indefinitely --> we will face unacceptable outcomes
LEADS TO
Final Conclusion: Mandatory retirement should be retained
(E) is necessary! Negation: If retirement ceases, nobody will choose to work past 65. Oh, then all those consequences won’t actually happen!
As for the incorrect answers:
(A) Tricky! Let’s negate it: some folks that have worked 40 years are under 65 yrs. old. Does this mean we can’t get to intermediate conclusion? No, we can still get there since the outcomes of the 65+ crowd would still be unacceptable.
(B) “Highly trained” is an easy reason to eliminate this answer. The argument is about those who trained for a role. Even if (B) did not shift the topic, it’s not important to this argument applies to all young people.
(C) Doesn’t the negated for of (C) undo the relationship in the premise? No, the premise about fairness is about having opportunities blocked (not about training). Another angle on this answer choice: what if you’re trained but really unprofessional? According to (C), it’s unfair if you don’t get a job for which you trained.
(D) Another tempting answer. If people are forced to retire at 65…wait, this argument is about what happens if they’re NOT required. This answer provides a nice example of a choice in which all concepts are mentioned (though perhaps the wrong side of them—who cares about older people’s dissatisfaction) but that is nonetheless out of scope.
#officialexplanation