The people,_had been damaged by the flood ,were given help by the Red Cross.

问题描述:

The people,_had been damaged by the flood ,were given help by the Red Cross.
The people,_had been damaged by the flood ,were given help by the Red Cross.
A.all whose homes
B.all of whose home
C.all their homes
D.all of their homes
.

选B,但home要加s.
all of whose homes 是非限定性定语从句,故用whose 替代their,也就是先行词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.
你的题中,两逗号间的内容是起补充说明的作用,叫定语从句,全句的主句是:The people were given help by the Red Cross,补充的是定语从句,all of their homes had been damaged by the flood.但做定语要用关系代词whose 替代their,以避免重复.