单选题 In this passage, the author is primarily concerned with

• (A) advancing an argument against human cloning based on evidence from cloning experiments performed on lower life forms
• (B) measuring the technical and ethical limitations of the embryonic cloning process in mammals
• (C) refuting arguments against human cloning through the use of hard scientific evidence
• (D) illuminating the critical ethical distinctions in process between human cloning and sheep cloning
• (E) describing how the ethical issues in the quest for human cloning have given rise to new models of embryonic development