4.5 billion years as a regular number

Convection currents are caused by differences in what two things?

Blood pressure the total amount of blood the heart pumps in one minute 2. cardiac output the number of times your heart beats in a minute 3. dilate the amount of blood that the heart can pump in a single beat 4. heart rate the force exerted on the walls of the blood vessels by the blood that moves through them 5. stroke volume to widen or get larger in size

The diagram shows a boulder rolling down a hill into a valley and then up the opposite hill. at which position does the boulder have the greatest kinetic energy? a b c d