Which Statements Regarding the Preclinical Research Stage of Drug Development

Which statements regarding the preclinical research stage of drug development are true?

A) Most drugs do not proceed past the preclinical stage because they are found to be too toxic or just ineffective.
B) At the end of the preclinical research stage, client variability is determined and potential drug-to-drug interactions are examined.
C) The preclinical stage of research involves extensive testing on animals in the laboratory to determine if the drug will cause harm to humans.
D) Preclinical research results are always inconclusive.
E) The Food and Drug Administration (FDA) is responsible for extensive testing for safety before the pharmaceutical company can begin the preclinical research stage of development.