At a recent conference on ancient DNA, one presentation opened with the claim that the field was now mature and could move ahead with confidence. This (i)_____ is (ii)_____, as demonstrated at the conference by the many presentations that notably lacked an adequate methodology for ensuring that DNA was uncontaminated by material that is more recent. In fact, ancient DNA research presents extreme technical difficulties, in part precisely because of the (iii)_____ of surviving DNA.
答案：B,E,G