e. None of the above
The Subnet Address is found by setting all of the host bits in an
address to 0. According to the mask, there are 7 host bits, so applying
this rule yields a subnet address of 193.243.12.0. However, closer
inspection yields that there is only one subnet bit in this Class C
address - therefore, this is an illegal address/mask pair.
Reference: Comer, Internetworking with TCP/IP, Chapter 16.