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

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

A.
RIPV1 and OSPF are classless routing protocols.

B.
Classful routing protocols send the subnet mask in routing updates.

C.
Automatic summarization at classful boundaries can cause problems on discontigous networks.

D.
EIGRP and OSPF are classful routing protocols and summarize routes by default.