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 discontinuous subnets.

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