It affects the watersheds period because gravity causes rivers to flow downward from higher elevation. A good portion of them are glacial meltwater. It can divert the courses of rivers because water takes the path of least resistance.
B
(without the control you won't know what a normal result would be without the independent variable).
When you inhale muscles increase the size of your chest and in process your lungs expand. The increase of volume decreases the pressure in the lungs thus air rushes in.
Your answer would be "nervous-mesoderm".