A medical researcher is using rats to do an experimental test to determine the appropriate dosage for a new cancer drug. Each rat will be given a different dosage of the drug. The oncologist will then measure the growth rate of the cancerous tumor. Which of the following best describes the input and output variables that will be used in this experiment? O Input: growth rate of tumor; Output: dosage of drug O Input: dosage of drug; Output: size of the rat O Input: size of the rat; Output: dosage of drug O Input: dosage of drug; Output: growth rate of tumor O Input: size of the rat; Output: growth rate of tumor