as/which in attributive clauses
Dear teachers, when 'as' and 'which' are used in attributive clauses, are there any differences? Can 'which' substitute 'as' in attributive clauses all the time? Thanks very much.
1) The two brothers were satisfied with this decision, as/which was agreed beforehand.
2) He was a foreigner, as/which I knew from his accent.
3) Her attitude to him was quite the same as/which it had always been.
4) Chen says China has 500 missiles aimed at Taiwan as(which?) is adding one missile every six days.
5) I prefer asynchronous communications, as(which?) I believe forums and emails are termed.