How did the skeleton change during bird evolution?

"The reduction in a bird's skeletal weight is largely a result of hollow construction of the skeleton. The fusion or loss of individual bones reduces the number of movable joints in the bird's skeleton, making it rigid and better adapted as the internal framework of a flying machine."

ya the other dude is right

the answer is z.

the human body has five levels of organization. level 1: cells. cells are the basic units of life and form the first level of organization. cells in the human body have specific functions. examples include nerve cells, blood cells, liver cells, and so on.