Birds have hollow bones due to the fact thay need to be as light as possible for their wings to generate enough lift for them to fly
<span>The correct answer to this question is the following:
The crust’s role in biogeochemical cycles allows it to provide the raw materials necessary for life on earth. The crust actually affects earth in a massive variety of ways, that are impossible for us to understand without the research undertaken by scientists to understand more about its' effects on life.</span>
Answer:
rise over run
Explanation:
rise refers to the number of units going u or down a graph
run refers to the number of units going left or right
it is seen as so;
,
, or 
Don't panic when I included "delta". Delta, it refers/means the small mathematical triangle found beside the rise and run symbols of y and x
They are cerebral ventricles