You are planning an experiment to estimate how the average length of time that a bacterial colony can survive changes with the dosage of antibiotics they are treated with, and only have the resources to test 30 colonies. Which of the following methods would give you the most precise estimate of the change in survival time with dosage, assuming that all the assumptions of linear regression are met? Remember that the standard error for a regression slope is residuals and is the predictor variable. (n-1) . Select one: a. Give 15 colonies a dosage of 0 mg and 15 a dosage of 200 mg where is the Ob. Give all 30 colonies a dosage of 200 mg c. Give each colony a different dosage, with dosages spread evenly between 0 mg and 200 mg d. Give 15 colonies a dosage of 50 mg and 15 a dosage of 100 mg