Your company has a main office and two branch offices.The main office is located in Montreal.The branch offices are located in Seattle and Winnipeg. 
In the Montreal office, you have a server named Server1 that runs Windows Server 2003 Web Edition Service Pack 2 (SP2).Server1 is configured as a VPN router. 
In the Seattle office, you have a VPN server named Server2. In the Winnipeg office, you have a VPN server named Server3. 
On Server1, you configure a L2TP/IPSec demand-dial interface for each branch office.On each branch office server, you create a single demand-dial interface that uses L2TP/IPSec to connect to the main office. All demand-dial interfaces are configured to use a pre-shared key. 
You discover that only one branch office can connect to the main office at a time. 
You need to ensure that both branch offices can connect to the main office simultaneously. 
What should you do? 
A.
Add two more demand-dial interfaces on Server1. 
B.
Install a computer certificate on Server1, Server2, and Server3. 
C.
Upgrade Server1 to Windows Server 2003 Standard Edition SP2. 
D.
Add an additional demand-dial interface on Server2 and Server3.