[root@localhost ~]# mkdir .first [root@localhost ~]# cd .first [root@localhost .test]# mkdir .second [root@localhost .test]# cd .. [root@localhost ~]# free > .free.txt [root@localhost ~]# cp .free.txt...

[root@localhost ~]# mkdir .first
[root@localhost ~]# cd .first
[root@localhost .test]# mkdir .second [root@localhost .test]# cd ..
[root@localhost ~]# free > .free.txt [root@localhost ~]# cp .free.txt ~/.first/.second
Refer to the above exhibit. Which one of the following command is used to display files of "second" directory?
a. ls-a
b. ls -r -a c. ls
d. ls -R -a