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针对语法选择题，关键在于快速抓住题干的关键词，理解题干意思，如：（来源：2013年东北师范大学考博英语真题）
If I ______ work harder at school, I would be sitting in a comfortable office now.
针对此题，根据题干中“ I ______ work harder at school（在学校学习更努力的话）”和“sitting in a comfortable office now（现在就会在舒服的办公室里坐着）”可知，从句中的“at school”相对主句中的“now”而言为过去的情况，根据if虚拟语气的语法规则，可知正确答案为选项C。
补充：if 虚拟语气的语法规则
If I ______ work harder at school, I would be sitting in a comfortable office now.
- worked B. were to work C. had worked D. were working
针对此题，根据题干中“ I ______ work harder at school（在学校学习更努力的话）”和“sitting in a comfortable office now（现在就会在舒服的办公室里坐着）”可知，从句中的“at school”相对主句中的“now”而言为过去的情况，根据if虚拟语气的语法规则，可知正确答案为选项C。
补充：if 虚拟语气的语法规则
| 使用条件 | 从句的时态 | 主句动词的情况 |
| 与现在事实相反 | 一般过去时（be动词一般用were） | would/should/might/could+V原 |
| 与过去事实相反 | 过去完成时 | would/should/might/could+ have +V过去分词 |
与将来事实相反 |
|
would/should/might/could+V原 |
