单选题 The repairperson could not find the specific problem ______ had caused the computer to crash.
A. how B. whom C. what D. that

【正确答案】 D
【答案解析】[解析] 通过分析句子结构，空格前为主语+动词+宾语的结构，因此空格以后的都必须为修饰先行词problem的关系代词从句。