You need to ensure that the virtual host can connect to the physical network

You have a server that runs Windows Server 2008 R2.
The server has the Hyper-V server role installed.
You create a new virtual machine and perform an installation of Windows Server 2003 on the virtual machine.
You configure the virtual machine to use the physical network card of the host server.
You notice that you are unable to access network resources from the virtual machine.

You need to ensure that the virtual host can connect to the physical network.

What should you do?

A.
On the host server, install the Microsoft Loopback adapter.

B.
On the host server, enable the Multipath I/O feature.

C.
On the virtual machine, install the Microsoft Loopback adapter.

D.
On the virtual machine, install Microsoft Hyper-V Integration Components.

Explanation:
Networking and virtual machines
To connect a virtual machine to a virtual network, you add a virtual network adapter to the virtual machine and then connect the virtual network adapter to an existing virtual network.
There are two types of network adapters available for Hyper-V: a network adapter and a legacy network adapter.
The network adapter is designed specifically for Hyper-V and requires a virtual machine driver that is included with the Hyper-V integration services. This type of networking adapter provides better performance than a legacy network adapter and is the recommended choice when it can be used. Because this type of virtual network adapter requires integration services in the guest operating system, it can be used only with guest operating systems for which integration services are available.

Note If a network adapter is configured for a virtual machine but integration services are not installed in the guest operating system, Device Manager lists the network adapter as an unknown device.

Source: http://technet.microsoft.com/en-us/library/cc816585.aspx

Integration services
Integration services are available for supported guest operating systems as described in the following table.

Windows 2003 SP2 Guest operating system – Device and service support
* Windows Server 2003 (x64 editions) with Service Pack 2
Drivers: IDE, SCSI, networking, video, and mouse
Services: operating system shutdown, time synchronization, data exchange, heartbeat, and online backup
Note This operating system does not support a legacy network adapter.

* Windows Server 2003 (x86 editions) with Service Pack 2
Drivers: IDE, SCSI, networking, video, and mouse
Services: operating system shutdown, time synchronization, data exchange, heartbeat, and online backup

Source: http://technet.microsoft.com/en-us/library/cc794868(WS.10).aspx