選B,但home要加s.
all of whose homes 是非限定性定語從句,故用whose 替代their,也就是先行詞the people,all of the people's homes,all of their homes.
例如：The children,two of whose fathers are scientists,were invited to talk about their families.
你的題中,兩逗號間的內(nèi)容是起補充說明的作用,叫定語從句,全句的主句是：The people were given help by the Red Cross,補充的是定語從句,all of their homes had been damaged by the flood.但做定語要用關(guān)系代詞whose 替代their,以避免重復(fù).