[单项选择] While using the smit install_remove menus to remove some filesets on an AIX 5.3 server, a system administrator notices the /usr filesystem is now unnecessarily large. Which of the following actions will reduce the size of the /usr filesystem () A. Backup, unmount, remove, recreate and restore the filesystem. B. Boot from mksysb tape and select Shrink filesystems on restore. C. Unmount, run defragfs /usr and the reducefs -size n /usr commands. D. Update the /image.data file with the desired size for /usr and reboot the system.