The doctor ____ is leaving for Africa next month.A. the nurse is talking to himB. whom the nurse is talkingC. the nurse is talking toD. who the nurse is talking

本题考查定语从句的用法，核心在于正确识别关系词的省略和介词的搭配。
关键点：

1. 先行词是doctor，需判断关系词的类型（指人时通常用who/whom）。
2. talk to 是固定搭配，介词to不可省略。
3. 当关系词在从句中作宾语时，可以省略关系词，此时从句结构需完整。

选项分析

选项C

结构：the nurse is talking to

• 关系词whom省略（作宾语），完整形式为：the doctor whom the nurse is talking to。
• talk to 是固定搭配，介词to必须保留，使句子语法完整。

错误选项排除

• A：the nurse is talking to him
  • him是代词，不能替代关系词whom，且定语从句中不能单独使用代词。
• B：whom the nurse is talking
  • 缺少介词to，导致talk缺少宾语，结构不完整。
• D：who the nurse is talking
  • 同样缺少介词to，结构错误。