听力原文： Scientists have discovered evidence that a dinosaur found in Montana was a femal

e. Scientists have never before been able to reliably determine the sex of fossilized dinosaurs. The latest discovery gives them a tool to identify at least some females. What they found was a layer of something called medullary bone inside the thighbone of a dinosaur dug up five years ago. Scientists had cut the bone into two pieces to get it into a helicopter. Medullary bone is only known in ovulating birds, it's a source of calcium that birds draw to make shells for their eggs. Writing in the journal Science, the scientific team believes the bone layer could be a way to identify other female dinosaurs but only if they died while making eggs and were then fossilized. They point out that the discovery confirms the view that modem birds are the closest living relatives of the two-legged dinosaurs.

Which is NOT correct description about Medullary bone？

A．Medullary bone is only known in ovulating birds before.

B．It is full of calcium.

C．Birds draw calcium in it to make shells for their eggs.

D．A dinosaur doesn't have medullary bone.