Which statement is true, as relates to classful or classless routing?

Which statement is true, as relates to classful or classless routing?
A . Classful routing protocols send the subnet mask in routing updates.
B . RIPv1 and OSPF are classless routing protocols.
C . Automatic summarization at classful boundaries can cause problems on discontiguous subnets.
D . EIGRP and OSPF are classful routing protocols and summarize routes by default.

Answer: C

Explanation:

http://www.ciscopress.com/articles/article.asp?p=174107&seqNum=3

RIPv1, RIPv2, IGRP, and EIGRP all auto-summarize classful boundaries by default (OSPF does not).To make discontiguous networks work, meaning you don’t want classful boundries to summarize, you need to turn off auto-summary.