9. Pharmaceutical companies are selling billions of dollars' worth of single-enantiomer drugs. Why might it be important to use only one form of an enantiomer? (A) One enantiomer may provide an effective treatment whereas the other may be ineffective or even toxic. (B) It is cheaper to manufacture only one of the enantiomers. (C) The left-handed version of the enantiomer is always the effective one. (D) It is not important. Both enantiomers will be equally effective. (E) All of the listed responses are true.