In What Way Are Monotremes Similar to More Ancestral Chordate

In what way are monotremes similar to more ancestral chordate lineages,as opposed to more recently evolved mammals?

A) Monotremes lay eggs;other mammals bear live young.
B) Monotremes perform little parental care;other mammals use lactation to feed offspring.
C) Monotremes do not have jaws;other mammals do.
D) Monotremes exchange gases through their skin;other mammals use lungs.
E) Monotremes perform external fertilization;other mammals perform internal fertilization.