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A student wants to answer the question "Does adding calcium powder to soil make pea plants grow faster?" She adds calcium
powder to the soil of 12 plants and does not add it to the soil of a second group of 12 plants. She measures the growth of all of
the plants in each group for a month. Which statement best summarizes the factors that need to be controlled in this
experiment?
A

because they are eaten by the frog and the frog getseaten by the snake and the snake by the eagle

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.