∵Rt△ABC rotates 90 around point O to get Rt△BDE,
∴OA=OB=OD,∠AOB=∠BOD=90，
∴△AOB and △BOD are isosceles right triangles,
∴∠ABO=∠OBD=45，
∴∠ABD=45 +45 =90，
∵∠ ABC+∠ DBE = 90，
Points b, c and e are on the same straight line.
The rotation angle is 90 degrees,
∴△COE is an isosceles right triangle,
AC = 6，AB= 10，
∴BC=AB2？ AC2= 102？ 62=8,
∴CE=BC+BE=8+6= 14，
∴OC=22CE=22× 14=72.
So choose a.