O is for ... ostrich!

Well, not the whole ostrich - it wouldn't fit in the drawer! The ostrich is the largest bird alive today - its eggs are about 20 times the size of hen eggs.

Question: The ostrich is the biggest bird alive today, but even bigger birds have lived in the past. Which of these extinct birds were bigger than an ostrich:

a. The moa
b. The dodo
c. The elephant bird