The sentence "Had he known her address, he would have written to her" means that
【正确答案】 C
【答案解析】虚拟条件句的省略与倒装形式，完整表达是if he had known her address。这是对过去事实的虚拟，故甩过去完成时，他实际上并不知道她的地址，答案为C。