関連ワード:
the bones of birds are hollow true or false the bones of most birds are hollow true or false the bones of birds are light and hollow true or false the bones of birds are hollow and filled with air true or false the hollow bones of birds help them fly true or false birds can fly because their bones are hollow true or false the birds have hollow bones true or false are the bones of birds hollow why do birds have hollow bones hollow bones of birds are called
