Which of the following is a testable hypothesis?

The friction red blood cells encounter when moving past each other. cardiac output: the amount of friction blood encounters during flow through blood vessels. blood pressure: the force of the blood against the vessel wall. blood viscosity: the volume of blood pumped out by one ventricle each minute.

In general, characteristics that an organism survive and reproduce become more common over time. what mechanism of evolution causes this?

How does photosynthesis show the conservation of mass and energy?