Sand blowing against a rock is an example of erosion
physical weathering
chemical weathering

answer///multiple alleles;

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.

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.