Thx Friend ,
Actually I already try to use the following lines :
# ServerName www.example.com:80
But the page cannot be displayed . But when I use just "server.example.com" then it is working . My web server is my DNS server and my /etc/hosts is :
[root@localhost ~]# cat /etc/hosts
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6
do u plz tell me where is the problem ?