A primitive streak forms during the early embryonic development ...

[sammy]

A primitive streak forms during the early embryonic development of
A) birds, but not frogs or humans.
B) frogs, but not birds or humans.
C) humans, but not birds or frogs.
D) birds and frogs, but not humans.
E) humans and birds, but not frogs.

[clippers!]

I remember it was E