A system administrator has been asked to migrate the dev_vg volume group from server A to server B. The dev_vg volume group contains a single filesystem named "/development". To prepare for migration， which of the following is the correct sequence of commands for removing the volume group from server A？（）

A.exportvg dev_vg； umount /development； varyoffvg dev_vg
B.varyoffvg dev_vg； umount /development； exportvg dev_vg
C.umount /development； exportvg dev_vg； varyoffvg dev_vg
D.umount /development； varyoffvg dev_vg； exportvg dev_vg