A.grep root /etc/group B.echo root ∣grep /etc/group C.echo /etc/group ∣grep root D.A和C
A.echo ftp /etc/services B.echo ftp < /etc/services C.grep ftp -q /etc/services D.grep ftp < /etc/services
A.grep–n sun /usr/share/dict/words B.grep–N /usr/share/dict/words sun C.grep–r sun /usr/share/dict/words D.grep–r /usr/share/dict/words sun