Why (D) is right: the one decisive fact
A Sufficient assumption explanation from our free library. The question below is original, written for this page. Then the full breakdown: why the right answer is right, and why each wrong answer is wrong.
The question
The committee approves a proposal only if every member votes yes. Ana is a member of the committee. Therefore, the proposal will not be approved.
Which one of the following, if assumed, allows the conclusion to follow logically?
- Ana disagrees with the proposal.
- Most members of the committee will vote yes.
- The committee rarely approves proposals.
- Ana will vote no. Correct
- Ana is the most senior member of the committee.
Why (D) is correct
The rule is strict: approval requires every member to vote yes. One no vote anywhere kills the proposal. Choice (D) supplies exactly one no vote, from Ana, who is a member.
With (D) in place, 'every member votes yes' is false, so the 'only if' condition fails, and rejection follows by logic alone. (A) is the trap to study: on the LSAT, disagreeing, leaning, and tending are never the same as doing. Only the actual vote counts.
Why the wrong answers are wrong
(A) Half-right
Disagreeing is not voting. Ana might disagree and still vote yes, or abstain. This does not guarantee the outcome.
(B) Too weak
'Most' is not 'every.' This leaves open the possibility that every member votes yes, which is exactly what the conclusion denies.
(C) True but irrelevant
A track record of rejection does not prove this proposal will be rejected. General tendencies do not decide a specific vote.
(E) Out of scope
Seniority has no stated connection to voting rules. The argument is about votes, not rank.
Last updated October 12, 2026