Asystemadministratorhasbeenaskedtomigratethedev_vgvolumegroupfromserverAtoserverB.Thedev_vgvolumegroupcontainsasinglefilesystemnamed"/development".Toprepareformigration，whichofthefollowingisthecorrectsequenceofcommandsforremovingthevolumegroupfromserverA？（）
A.exportvgdev_vg；umount/development；varyoffvgdev_vg
B.varyoffvgdev_vg；umount/development；exportvgdev_vg
C.umount/development；exportvgdev_vg；varyoffvgdev_vg
D.umount/development；varyoffvgdev_vg；exportvgdev_vg