DRAG DROP
Your network contains an Active Directory forest named corp.contoso.com. All servers run
Windows Server 2012.
The network has a perimeter network that contains servers that are accessed from the
Internet by using the contoso.com namespace.
The network contains four DNS servers. The servers are configured as shown in the following table.
All of the client computers on the perimeter network use Server1 and Server2 for name
resolution.
You plan to add DNS servers to the corp.contoso.com domain.
You need to ensure that the client computers automatically use the additional name servers.
The solution must ensure that only computers on the perimeter network can resolve names
in the corp.contoso.com domain.
Which DNS configuration should you implement on Server1 and Server2?
To answer, drag the appropriate DNS configuration to the correct location in the answer
area. Each DNS configuration may be used once, more than once, or not at all. Additionally,
you may need to drag the split bar between panes or scroll to view content.
Answer: 
Explanation:
Correct: child domain use stubzone
So when to use stub versus zone delegation?
Don’t understand, who can help to explain.
What does “You need to ensure that the client computers automatically use the additional name servers.” refer to?
Does “You need to ensure that the client computers automatically use the additional name servers.” refer to stub zone? The reason is stub zone is dynamic ? Anybody agrees?
Let me try to explain.
The computers on the perimiter network have are the only ones that may resolve hosts in corp.contoso.com.
Computers from the internet will go to contoso.com (Server1 or Server2) to findout how to get to corp.contoso.com.
The StubZone for corp.contoso.com only has information about the Authoritative DNS Server for that zone.
A client DNS request is recursive. So Server1 or Server2 need to return the answer or an error message. They cannot return the address of a different server.
This way we fulfill the requirements.
A Conditional Forwarder would work but is Static and does not fulfill the requirements.
A Zone Delegation is used for Management of the DNS Zone.
A SubZone is a Unix concept.
SubZone should be SubDomain