Critical reasoning — identify implicit assumptions: Statement: Highly brilliant and industrious students do not always excel in written examinations. Assumptions: I. Written examinations are good mainly for mediocre students. II. Brilliant and industrious students cannot always write good answers in the exam.

Introduction / Context:
The statement contrasts underlying ability and effort with exam performance, claiming that even very capable and hardworking students sometimes do not excel in written tests. The task is to identify which assumptions must hold for this observation to be reasonable.

Given Data / Assumptions:

• Claim: Some brilliant, industrious students do not always achieve top scores in written exams.
• Assumption I: Written exams primarily favor mediocre students.
• Assumption II: Even brilliant and industrious students may fail to produce excellent written answers consistently.

Concept / Approach:
To make sense of the claim, we need only accept that exam performance depends on more than brilliance and industry, such as test technique, time management, stress, or alignment with marking schemes. That aligns with Assumption II. Assumption I is an exaggerated generalization and not necessary.

Step-by-Step Solution:

Verification / Alternative check:
Negate II: If brilliant and industrious students always write excellent answers, the statement becomes false. Negate I: Even if exams favor top students, they could still occasionally underperform; the original statement stands.

Why Other Options Are Wrong:

• Only I, Either, Both: These attribute an unnecessary global property to exams.
• Neither: Overlooks the minimal requirement captured by II.

Common Pitfalls:
Reading “do not always” as “never,” or smuggling in sweeping criticisms of exam systems not needed for the claim.

Final Answer:
Only assumption II is implicit