主句是：They do not have one exception
这是定语从句,完整的是：They do not have one exception which is foreigner.
他是把which省略了.
foreigner是修饰one exception ,所以用单数
主句是：They do not have one exception
这是定语从句,完整的是：They do not have one exception which is foreigner.
他是把which省略了.
foreigner是修饰one exception ,所以用单数