Which sequence best describes how a convection current forms in the air? A. Cold air rises. - Air warms up.
Warm air sinks.
B. Warm air rises.
Air gets warmer.
Warm air sinks.
C. Cold air rises. - Air gets cooler. - Cool air rises.
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D. Warm air rises. - Air cools off. - Cool air sinks.

the american rail road was the most influential and useful transportation system developed in the 1800's with steam locomotives and in the very late 1800's and early 1900's diesel electric locomotives being used to transport goods and people around the newly expanded united states!

it should be a. song dynasty’s civil service examination system created an administrative bureaucracy manned by the landed aristocracy.

the steam engine.

the locomotive.

the telephone.

the telegraph.

the internal combustion engine.

the rifle.

ironclad ships.

electricity/light bulb.