The A321 at 89,000 Kg MTOW is actually a Cat C aircrfat - it's only the heavyweight ones at 93,000kg MTOW that are Cat D.
Actually it depends on the max landig weight. If you lower the max allowed landing weight from 77800kg (on the 321 HIGW) to 76900kg, if falls in the cat C category..
93500kg is the max t/o for the heavyweight ones..
BR
Buster