The correct answer is (A).
Analysis:
Premise: Leaders of all major parties oppose the agriculture bill
Conclusion: The bill will almost surely fail to pass
We need an answer that strengthens this prediction.
Option A: "Most bills that have not been supported by even one leader of a major party have not been passed into law"
This directly strengthens the argument. The agriculture bill has ZERO leader support (all leaders oppose it). Option A tells us that when bills lack support from even ONE leader, they typically fail. Since this bill has NO leader support at all, it fits perfectly within this pattern and strengthens the prediction that it will fail.
Why other options don't work:
Option E: "Most bills that have been passed into law were supported by at least one leader of a major party"
This is NOT the contrapositive of A. Option E tells us what passed bills typically HAD (at least one leader's support), but it doesn't tell us what happens to bills WITHOUT any leader support. Just because most passed bills had support doesn't mean bills without support will fail - there could still be exceptions. E leaves open the possibility that some bills pass without leader support.
Option B: Focuses on "members" not "leaders" - wrong scope
Option C: This is a conditional (IF leaders endorse, THEN it passes), but it doesn't help us when leaders DON'T endorse. The contrapositive would tell us if it doesn't pass, then leaders didn't all endorse - but that doesn't strengthen our prediction.
Option D: Talks about bills that passed - opposite of what we need to strengthen.
The key distinction: A directly addresses what happens when bills LACK leader support (they typically fail), making it the strongest support for the prediction.