A system administrator would like to rename volume group oldvg to newvg. This volume group resides on hdisk1. What is the appropriate procedure to perform this？（）

A.reboot the server in maintenance mode；migratevg -y newvg oldvg；reboot the server in normal mode
B.unmount all filesystems in the volume group；varyoffvg oldvg；migratepv -y oldvg -n newvg  varyonvg newvg
C.unmount all filesystems in the volume group；varyoffvg oldvg；exportvg oldvg；importvg -y newvg hdisk1；mount all
D.unmount all filesystems in the volume group；varyoffvg oldvg；for each logical volume in the volume group do cplv -v oldvg -y newvg；varyonvg newvg；mount all