Often after the default installation of RHEL 7 or CentOS 7 on VirtualBox internet access or for that matter network connectivity don't work . The solution is simple. Just make the below edits
vi /etc/sysconfig/network-scripts/ifcfg-enp0s3
Change the entry
ONBOOT=no
to
ONBOOT=yes
reboot your machine or just restart network service.
Thats it !!! :)