In an experiment aimed at determining the corrosiveness of various acids, a controlled variable is something that must be kept constant throughout the experiment to ensure a fair test.
In this context:
- A. The acids used: This would be an independent variable since you are testing different types of acids.
- B. The material the acid is poured on: This should be a controlled variable, as you want to ensure that the only difference is the type of acid, not the type of material.
- C. The size of the hole created by the acid: This should also be a controlled variable, as it would ensure consistent measurement of corrosiveness.
Since options B and C are indeed controlled variables, and option A is an independent variable, the correct answer reflects that not all given options are controlled variables.
Thus, the best answer is: B. The material the acid is poured on (while C could be argued as controlled in context, it's not explicitly a given in the choices).
However, if you interpret "all of the above" as indicating a broader understanding that aspects related to measurement should be controlled, you could make a case for D. all of the above.
Ultimately, the most straightforward interpretation would lead to selecting B as the most definitive controlled variable.
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