单选题 Cet-6-3.13-Exercise.mp3 Questions 19 to 21 are based on the recording you have just heard.19. A) At museums of natural history in large cities.B) Science education and scientific research.C) Overseeing two research groups at Oxford.D) Along the border of the U.S. and Canada.20. A) Human beings have more obesity genes than most mice do.B) The function of the obesity genes is yet to be explored.C) Some natural disaster killed a whole herd of dinosaurs in the area.D) Volcanic explosions could bring whole animal species to extinction.21. A) They cannot be easily explained.B) They floated down an eastward flowing river.C) They can predict future events.D) They lay buried deep in the sand for millions of years Question 19