Yes !!
You can keep users of  different networks of class C in different Vlans connected with switches   and then perform Inter-vlan routing to make them communicate.

Cisco Discovery Protocol (CDP) is a proprietary layer 2 management protocol for networks. CDP provides network connectivity and device information. In real time networks CDP is use to find out about IP address of a  router or switch on the other side of a WAN link needed to take remote access of the device to troubleshoot problems or to configure device . CDP can be enabled/disabled at the inte... (more)

Just write  'NO' as prefix to the default route command:

Router(config)# no ip route 0.0.0.0 0.0.0.0 next-hop-ip/exit-interface

 

With SUBNETTING you will be able to get following results : 1st subnet : NETWORK ID - 10.0.0.0                                                 3rd subnet : NETWORK ID - 10.128.0.0                     BROADCAST ID- 10.63.255.255                                                    Â... (more)

D is the right answer.

Router : has Per-port broadcast domain & per-port collision domain.
Switch : has Single broadcast domain (by def) & per-port collision domain.

So, There are 2 broadcast domains & 5 Collision domains.