申请访学工签,一直没有消息,三个多月了。催签回复“Please be advised that your application is currently undergoing a standard background check. Please remain patient as this process may take longer than normal processing time. ” 请问这是正常的吗?已经过了邀请信的时间了,所以比较着急,不知道为什么会这么慢。是不是被加强版背景调查了?