One of the more unlikely offices to have been flooded with mail is that of the City University of New York (CUNY),
这句话的意思是 City University of New York (CUNY)是那些不太可能收到很多申请函但确实收到了很多申请函的大学办公室之一
unlikely 表示可能性不大
这句话可以写成 the office of the city university of new york(cuny)is one of the more unlikely offices to have been flooded with mail.
to 有修饰作用,修饰office the city university的办公室是这些办公室之一,怎么样的办公室?——officess to have been flooded with mail(被申请函淹没的办公室）