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Difficulty: HardMust Be True Questions

According to a recent ecological survey of the Veridian Basin:

Every tree species native to the Veridian Basin forms a symbiotic relationship with Mycena fungi. Any tree species that forms this symbiotic relationship requires highly acidic soil to thrive. Furthermore, most tree species currently cultivated in the newly established botanical gardens are native to the Veridian Basin. However, no tree species requiring highly acidic soil is tolerant of elevated soil salinity, even though at least some tree species tolerant of elevated soil salinity are successfully cultivated in the botanical gardens.

Based on the statements above, which of the following must be true? (Select all that apply.)

  1. Most tree species cultivated in the newly established botanical gardens are not tolerant of elevated soil salinity.Answer
  2. At least some tree species cultivated in the newly established botanical gardens do not form a symbiotic relationship with Mycena fungi.Answer
  3. C
    Any tree species that requires highly acidic soil to thrive is native to the Veridian Basin.
  4. D
    Tree species that are not native to the Veridian Basin cannot require highly acidic soil to thrive.
  5. E
    Every tree species cultivated in the newly established botanical gardens requires highly acidic soil to thrive.

Answer

The correct answers are the statements that 'most tree species cultivated in the newly established botanical gardens are not tolerant of elevated soil salinity' and 'at least some tree species cultivated in the newly established botanical gardens do not form a symbiotic relationship with Mycena fungi'.
Both correct statements are logically guaranteed by the text. The first correct statement is true because the 'most' quantifier carries through the conditional chain: if most garden trees are native, and all native trees ultimately cannot tolerate salinity, then most garden trees cannot tolerate salinity. The second correct statement is true because the text explicitly states some garden trees are tolerant of salinity. Taking the contrapositive of the established chain, any tree tolerant of salinity cannot require acidic soil, and therefore cannot form the Mycena symbiosis.

Step-by-Step Solution

1
Map the universal conditional statements provided in the stimulus.
Native -> Mycena -> Acidic Soil -> NOT Saline Tolerant.
Tracking conditional chains allows us to see the absolute guarantees that flow from one characteristic to another.
2
Apply the 'Most' quantifier to the conditional chain.
Since MOST cultivated trees are Native, MOST cultivated trees trigger the entire chain: Mycena -> Acidic -> NOT Saline Tolerant.
When a subgroup defined by 'most' enters a conditional chain, the final necessary condition applies to 'most' of that subgroup.
3
Evaluate the 'Some' statement using the contrapositive of the chain.
SOME cultivated trees are Saline Tolerant. Saline Tolerant -> NOT Acidic Soil -> NOT Mycena -> NOT Native.
Applying the contrapositive to the subgroup of salinity-tolerant cultivated trees proves that they lack the prior necessary conditions in the chain.
4
Match deduced conclusions to the options.
The deduction from Step 2 matches the option regarding most cultivated trees lacking salinity tolerance. The deduction from Step 3 matches the option regarding some cultivated trees lacking the Mycena relationship.
Correct Must Be True options must be 100% deducible strictly from the mapped text.

Key Concept

Chaining Conditional Logic with Overlapping Quantifiers
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