The famous scientist Albert Einstein sometimes used "thought experiments" such as imagining himself chasing a beam of light or riding in an elevator in free-fall. These thought experiments, which would not be possible to conduct physically, helped him challenge current scientific thinking and develop his theories of gravity and of special relativity.

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the answer would be knowledge about cars!

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.

the solute can move "downhill," from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. this process is called passive transport or facilitated diffusion, and does not require energy.