Choose the four variables that are most important to control in an experiment about the rate at which bread turns moldy.

To compare how quickly bread molds, keep conditions that directly affect mold growth the same. Humidity, the bread’s age, its type, and the storage container can all influence how quickly mold develops, so these are the four important variables to control. Time of day, observer height, bread shape, and shelf surface are not as directly relevant when the bread is stored and observed consistently.

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