What is the most common threat to the human body from an invading virus? b. acid will ferment in the digestive system c. viral reproduction will destroy one healthy cells d. muscle tone in the heart will be stimulated

imagine a line passing through the center of earth that goes through both the north pole and the south pole. this imaginary line is called an axis. earth spins around its axis, just as a top spins around its spindle. this spinning movement is called earth's rotation. at the same time that the earth spins on its axis, it also orbits, or revolves around the sun. this movement is called revolution.