I'm studying for CCNA using two guides, the Todd Lammie/Sybex book and the Wendell Odom/Cisco Certification Guides. They seem to be inconsistent in thier assuption of subnet zero. In the actual exam, if it is not stated, what should be assumed? That is if the anser is ambiguous.
I think there is nothing wrong with reading different books for the same exam, IMO it's more a time constrain and maybe something that wasn't understood in one book will be made clear in another book.
But for your ip subnet-zero question:
As of Cisco IOS Software Release 12.0, Cisco routers now have ip subnet-zero enabled by default, but if the network engineer feels that it is unsafe to use subnet zero, the no ip subnet-zero command can be used to restrict the use of subnet zero addresses.
As Cisco's IOS is these days at version 12.4 it would be save to assume that "ip subnet-zero" is enabled by default. The exam should tell you if it is disabled. I think IOS 12.0 was around in 2001 or so.