Logical reasoning PrepTest 147 · Section 4 · Question 23

Incorrect. There's no indication that H. subflexa needs linolenic acid, so even though they don't get any in their diet, we don't know that they synthesize it—they may just live without it.

Correct. Argument or Facts:
Facts

Question Type:
Must Be True

Stimulus Summary:

(1) Eaten by H. subflexa → Physalis
(2) Physalis → not Linolenic acid
(3) Growth/maturation of some insects → Linolenic acid
(4) Production of volicitin → Linolenic acid in diet
(5) Caterpillar species-most-Volicitin in saliva
(6) H. subflexa → not Volicitin in saliva

Answer Anticipation:
That's probably more than you ever expected to learn about caterpillars!

Here, there are a lot of statements that set out something as required for another, so those can be diagrammed as conditionals (with the required thing as the necessary thing). Looking at them, a lot talk about linolenic acid and volicitin, so we can look for connections that would allow an inference to be drawn.

Looking at the statements, there is some overlap with 1, 2, and 4, letting us infer that H. subflexa can't produce volicitin—but the stimulus already gave us that inference in the last clause. Separately, statements 5 and 4 work together to let us infer that most caterpillar species get linolenic acid in their diet.

Let's not get too bogged down in making as many inferences as possible up front! When there are 6 (6!) statements, it's often faster to "back-solve" by heading to the answers to see what you can support based on your diagrammed statements.

Answer Explanation:
Most species of caterpillars have volicitin in their saliva, and volicitin requires linolenic acid. Therefore, most species of caterpillars must have sources of linolenic acid in their diets! This answer is inferrable, so it's the correct answer.

Key Takeaway:
When there are many conditional statements and combinations would be numerous and difficult, a good process can involve heading straight to the answers and then seeing if you can justify it based on the premises. After all, only one valid combination of the premises will be correct, so spending time making several inferences is going to necessarily result in you making inferences that don't help you find a correct answer.

Incorrect. Linolenic acid is necessary for the production of volicitin, it's not established to be sufficient. Therefore, there may be butterflies that eat something with linolenic acid but fail to convert it to volicitin.

Incorrect. Something being poisonous is out of scope of the argument. While H. subflexa don't naturally eat anything with linolenic acid, it's possible that they'd be just fine if they did eat something with it.

Incorrect. There's no discussion of the Physalis plant being limited to H. subflexa, so this answer is unsupported.