Boulders can become smaller as they are moved down a stream bed. this is an example of the process of the wearing away of rock by grinding action.

The answer is weathering. Weathering is where rocks or other materials are broken down because of forces like wind or water. This is different than erosion, which is the process where the broken down materials are moved.

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.

d is the best answer for this question.