Which tense should be used to describe an experiment completed in 1990 with present relevance?
答案解析
**Core concept**: Tense usage (时态选择)
**Analysis**: The simple past tense describes completed actions at specific past times.
**Correct answer**: B. The specific time marker 'in 1990' requires simple past.
**Error analysis**: A. Present perfect connects past to present without time markers; C. Past perfect requires another past reference; D. Continuous aspect describes ongoing actions.
**Key indicator**: The explicit time phrase 'in 1990' dictates tense choice.
正确答案：B