The research described in the passage is primarily concerned with answering which of the following questions？

A. What research guarantees the reality of the effects that hypnosis has on brain activity, and what is their causal mechanism？
B. How are experiments devoted to disproving the "vivid imagination"objection to hypnosis different from those devoted to disproving the"placebo effecfthesis？
C. How can researchers reproduce the useful effects of hypnosis in a medical setting？
D. What technical advances have permitted researchers to reject skeptical explanations of the phenomenon of hypnosis？