Which word is closest in meaning to 'sphere' when referring to a field of activity?
答案解析
Core concept: Semantic meaning of 'sphere' (metaphorical usage).
Correct answer: C. 'Domain' matches the abstract 'field of activity' sense.
Error analysis: A/B/D refer to physical round objects.
Key distinction: Concrete vs. abstract meanings of spherical terms.
正确答案：C