PrepTest 152, Section 1, Question 10
When a bird flies, powerful forces converge on(46 more words not shown)
Which one of the following(5 more words not shown)
- Athe only structure(6 more words not shown)
- Bthe reason that(9 more words not shown)
- Cthe sole connection(7 more words not shown)
- Dthe source of(9 more words not shown)
- Ethe means by(8 more words not shown)
Reading the argument
That ligament has a demanding job. Flight puts powerful forces on the shoulder joint, and the ligament is the only structure that can balance them.
What we’re looking for
My first thought is that the ligament must be dealing with those powerful forces. That's a reasonable starting point, but the completion needs to follow from the specific facts we've been given. We shouldn't leap to something like 'the ligament is often injured.' Stress on a joint doesn't tell us how often injury occurs.
Working the answers
- A
Being the only structure capable of balancing these forces doesn't make the ligament the only structure indispensable to flight. Other structures could be needed for different jobs. The argument identifies one exclusive role, not the only thing a bird needs in order to fly.
- B
This confuses the means of achieving stability with the reason stability is required. The ligament balances the forces so the wings can stay stable. Its existence doesn't explain why a bird needs stable wings during flight; the passage gives us that need as a starting fact.
- C
The passage says this ligament connects the wing to the shoulder joint, but it doesn't say nothing else connects them. The 'only' claim concerns the ability to balance the forces. Another connection could exist without having that ability, so C extends the claim beyond what we know.
- D
Balancing a force isn't the same as producing it. We're told the ligament handles the forces that converge on the joint, not that it generates those forces. We don't need an outside account of where they come from to see that the passage hasn't identified the ligament as their source.
- ECorrect
This is more precise than my initial thought about the ligament being under force. The wings must stay stable, stability requires the forces to be balanced, and only this ligament can balance them. The ligament therefore provides the means of stabilizing the wings during flight. Each step comes from the passage; we haven't added a claim about injuries, other connections, or where the forces originate.
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