Chapter 2, Problem 2.15.2C

Please explain why other options are incorrect

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Control variables, are those that the investigator does not want to vary systematically with the independent variable. The control variable should remain constant throughout the experiment. Let us examine an actual experiment to clarify the principles of the scientific investigation. Suppose a scientist is interested in studying the relationship between the color of light and photosynthesis in plants. From previous research, the experimenter knows that light is necessary for photosynthesis and that oxygen gas is produced as a by-product. The sunlight needed for photosynthesis, as well as the light from artificial sources such as light bulbs, is white light. White light is composed of all the different colors of the visible light spectrum. By using a prism, a solid triangular piece of glass, white light can be separated into its many wavelengths. The wavelengths become visible as different colors. Not all wavelengths are absorbed and used by green plants for photosynthesis. Some…