Answer:
An object decreases in size due to the collision of materials. An object increases in size due to the addition of materials. Gas particles are formed from solar nebula materials.
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Two things make up a vector: magnitude and direction.
Two vectors having the same magnitude doesn't guarantee that they have the same direction, and therefore it's not a guarantee that they are equal.
B. The sun was in the center of Ptolemy's model, but the Earth was in the center of Copernicus' model.