At which altitude did the atmosphere show the strongest evidence of condensation and energy transfer that helped the storm grow?

Condensation is most clearly indicated by visible water droplets forming in clouds, and the strongest upward motion helps carry moist air upward as the storm grows. Choice D places both clues at 4.0 kilometers: very moist air, the strongest upward motion, and visible droplets forming. The other choices describe weaker upward motion or cloud formation that is only beginning.

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