I’m a Chinese student major in Archive Science. In China, we have a system that regardless of the records’ classification level, all records which transfer to Archives have to keep for 30 years. After 30 years keeping, only then will the Archives assess again whether open those records to public. Some Chinese experts said this system which we called“closing period”came from the United States, but I can’t find any documents about it. So I ask for your help to know whether the United States has such a system？If have, set up the closing period for what reasons? Where I can find relevant documents? I sincerely appreciate your help.