Rahul sees a flock of birds. He watches as the flying birds land in neat little rows on several power lines. Which change of state does the motion of the birds most closely model?

As the birds fly, they are spread out like particles in a gas. When they land in neat rows, they become arranged closely together, like particles changing directly from a gas to a solid. That change is deposition; melting and vaporization involve liquids, while sublimation is the reverse of deposition.

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