The Nurse Explains to a Student Nurse That the Median

The nurse explains to a student nurse that the median lethal dose of drugs is often determined in laboratory preclinical trials because

A) it would be unethical to determine these values in human subjects.
B) the safety of the medication must be determined prior to clinical trials.
C) it is difficult to obtain sufficient participants for clinical trials.
D) clinical trials determine only the effective dose of a drug.
E) it is too costly to conduct the studies during clinical trials.