请教大全128，谢谢

1.
            As it becomes more frequent to have spouses who both work outside the home, companies are beginning to help in finding new employment for the spouses of transferred employees.

(A) it becomes more frequent to have spouses who both work outside the home

(B) it becomes more frequent to have couples both working outside the home

(C) it becomes more common that both husband and wife should be working outside the home

(D) it becomes more common for both husband and wife to work outside the home（D）

(E) couples in which both of the spouses working outside the home become more common

请教一下 ，D中IT究竟指代什么呢？

以前的讨论帖说指to work outside the home，但是我感觉应该指代for both husband and wife to work outside the home，但是IT不能指代介词短语啊，谢谢