A student hypothesized that robins prefer large birdhouses to small ones. He build four birdhouses of different sizes to test his hypothesis. What was the independent variable in the students study?

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some of your causes might be acidic rain or natural wildfires that cause the parks to be degraded

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enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products