all staff，all staffs Hello，Everyone！！ I don't know if I should pick a plural noun behind ”all” or singular in the following two sentences： The management has assured -------all staff -----that anyone attending the professional development seminars will receive a certificate thanking them for their participation. The management has assured -----all staffs-----that anyone attending the professional development seminars will receive a certificate thanking them for their participation. Thanks very much in advance ！