The bones of a bird are hollow why would this be an disadvantage for a bird

Which group of protists would be most likely to have cilia as adults and why? (1 point)the sporozoan protists would since they have to spread their spores around.the heterotrophic protists would since they use them to gather food.the parasitic protists would since they need to find other organisms to attack.the autotrophic protists would since they must move to find light.