According to msdn it is supported in SQL Server Enterprise 2005
"Peer-to-peer replication is available only in SQL Server 2005 Enterprise Edition."
This is true. But since the question asked which edition of SQL Server 2008 supported it, it's irrelevant.
The question was good, but had a minor flaw in presentation. Because it was single-choice, and the two relevant choices were Standard and Enterprise edition, all that was required to get a correct answer was the knowledge that Enterprise edition has all of the features of Standard edition and more. Therefore if Standard edition were a correct answer, then Enterprise edition would have to be as well. And if Standard edition were not correct, Enterprise is the only other option. So Enterprise edition has to be a correct answer.
So if you really want to test someone's knowledge of features in specific editions, a multiple-answer format really is necessary.