You need to ensure that all of the virtual machines that connect to Switch1 are isolated from the external network and can connect to each other only

Your network contains an Active Directory domain named contoso.com. The domain contains a member
server named Server 1. Server1 runs Windows Server 2012 R2 and has the Hyper-V server role installed.
You create an external virtual switch named Switch1.
Switch1 has the following configurations:
 Connection type: External network
 Single-root I/O virtualization (SR-IOV): Enabled
Ten virtual machines connect to Switch1.
You need to ensure that all of the virtual machines that connect to Switch1 are isolated from the
external network and can connect to each other only. The solution must minimize network downtime
for the virtual machines.
What should you do?

A.
Remove Switch1 and recreate Switch1 as an internal network.

B.
Change the Connection type of Switch1 to Private network.

C.
Change the Connection type of Switch1 to Internal network.

D.
Remove Switch1 and recreate Switch1 as a private network.

Explanation:
You can change the connection type of a virtual switch from the virtual switch manager without having
to remove it.
A private virtual network is isolated from all external network traffic on the virtualization server, as well
any network traffic between the management operating system and the external network.
This type of network is useful when you need to create an isolated networking environment, such as an
isolated test domain.

http://technet.microsoft.com/en-us/library/cc816585%28v=WS.10%29.aspx
http://blogs.technet.com/b/jhoward/archive/2008/06/17/hyper-v-what-are-the-uses-for-differenttypes-of-virtualnetworks.aspx