Which Statement Explains the Usefulness of the Median Toxicity Dose

Which statement explains the usefulness of the median toxicity dose best?

A) Is useful because drug amounts that are lower than the TD₅₀ will not produce the desired effect.
B) Is useful for determining the efficacy and potency of a drug.
C) Is useful because it is not ethical to determine the LD₅₀ in humans.
D) Is useful because drug amounts that exceed the TD₅₀ will be lethal to half the population.