A person who sees someone fall overboard should（）.
A. call for help and keep the individual in sight
B. run to the radio room to send an emergency message
C. immediately jump in the water to assist the individual
D. go to the bridge for the distress flare
UNIX操作系统的帐号管理和权限分配主要是通过哪三个文件管理来实现（）。
A. /etc/passwd，/etc/profile和/etc/group
B. /etc/group，/etc/profile和/etc/shadow
C. /etc/group，/etc/shadow和/etc/passwd
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