You want to place a piece of glass tubing into a ruber stopper after the tubing has been fire polished and cooled. This is best done by

c is the answer because when something is left after something evaporates that shows the chemical change.

warm front forms when a moist, warm air mass slides up and over a cold air mass. as the warm air mass rises, it condenses into a broad area of clouds. a warm front brings gentle rain or light snow, followed by warmer, milder weather.

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