<span>The answer is Due to heating of the air by the engine exhaust. Contrails are formed when the hot exhaust of the plane engines is rapidly cooled by the cold air in the upper atmosphere. The water vapor in the engine exhaust, formed in the combustion of fuel, freezes immediately to ice crystals due to the low pressure and -36oC temperatures in the 8000 m altitude in which the planes cruise. </span>
<span>Prokaryotic organisms are always unicellular, but eukaryotic organisms are always multicellular.
the second option because pro are usually found in plants and euk in animals and humans
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This might help:
https://quizlet.com/1965478/environmental-health-test-1-flash-cards/
