Need little help

hello everyone im studyng for the CCNA cert and i have a little lab witch consinst in to routers 2524 with de 5in1 serial connection ( with IOS 11.1) and one switch 1924. All of this equipment works extremely fine but i have this problem:

The network is configured this way

net-A :192.168.2.1
net-B :192.168.3.1
net-C :192.168.4.1

the problem is that i have active directory on my lab and the DHCP service is instaled on the net-A network, and on the net-C i have a server with a relay agent installed and im cant get a ip adrees form net-C. i now its a configuration problem and i hope someone can help me.