The residents, ________ had been damaged by the flood, were given help by the Red Cross．A. all their homesB. all whose homesC. all of whose homesD. all of their homes

步骤 1：分析句子结构
句子的主语是 "The residents"，谓语是 "were given help"，由 "by the Red Cross" 表示施动者。逗号前的部分是定语从句，修饰 "The residents"。

步骤 2：确定定语从句的先行词
先行词是 "The residents"，定语从句中需要一个关系代词来指代先行词。

步骤 3：分析定语从句的成分
定语从句中 "had been damaged by the flood" 是谓语部分，缺少主语。"all" 是定语从句的主语，"of whose homes" 是定语从句的主语的定语，修饰 "all"。

步骤 4：选择正确的选项
选项 A 和 D 中的 "their" 不能在定语从句中作关系代词，选项 B 中的 "whose" 可以作关系代词，但缺少 "of"，因此选项 C 是正确的。