You work as an administrator at ABC.com. The ABC.com network consists of a single domain named ABC.com. All servers in the ABC.com domain， including domain controllers， have Windows Server 2012 R2 installed.You add the DHCP Server Role on a server named ABC_SR04. You configure DHCP to support two subnets named Subnet A and Subnet B. Subnet A has a network ID of 172.16.0.0/16 and Subnet B has a network ID of 172.16.1.0/24.All client computers are reconfigured to receive IP addresses from DHCP. However， clients on Subnet B cannot access clients on Subnet A. What is the most likely cause of this problem？（）