Scientists hypothesize that a particular type of fat known as “P-fat” is required for the development of eyesight.
We're asked to support the scientists' hypothesis, so it will behoove us to treat that hypothesis as the conclusion, identify the evidence on which it is based, and try to identify holes in that argument that our strengthener might patch.
Conclusion
P-fat is required for the development of eyesight.
Evidence
Babies fed low-P-fat formula have worse eyesight than babies fed with mother's milk, which is high in P-fat. Babies that are 5-6 weeks premature have worse eyesight than those carried to term.
Evaluate
The first piece of evidence seems like pretty good support that P-fat contributes to eyesight development. But does it really prove that P-fat is necessary? That seems like a stretch. We might object that other differences between formula and mother's milk are to blame for the worse eyesight.
The second piece of evidence is even less helpful. What does being premature have to do with P-fat?
Anticipate
The right answer might strengthen this argument by connecting premature birth to P-fat in some way. If we knew that babies get more P-fat in utero than they do from milk after they're born, that would make this a better argument. But, because Strengthen questions aren't the most predictable, we'll still read every answer with an open mind.