when表示同时发生,或有先后.所有有时“when”可以换成“after”或"before"是的,一般结构是：had done sth...when...did但when的结构是灵活的,既可以将had done作为主句,可也以将did作为主句.所以：had done sth...wh...就是说这里可以用when 也可以用 after before是吗直接可以换成"after"，
They went home after they had spent all their money.
或倒过来可以用"before"
Before they went home, they had spent all their money.