46. What did the PLOS ONE study find at a site in the Sahara Desert?

　　A) Fishing tools.

　　B) Rock art works.

　　C) Human bones.

　　D) Animal remains.

　　47. By what evidence did researchers decide that the findings could be food waste of ancient people?

　　A) Traces of cutting and burning.

　　B) Estimated history of fish fossils.

　　C) Different specimens of wild animals.

　　D) Cooking tools found at the site.

　　48. According to Savino di Lernia, what’s peculiar about the findings in the research?

　　A) Ancient Africans fed on different kinds of food, including mammals.

　　B) Africa has been rich in wild animals since the prehistoric time.

　　C) Fish was once widely consumed as a food in early history of North Africa.

　　D) Many animals migrated regularly from North Africa to the Sahara Desert.

　　49. What did scientists find about the environment of the Acacus Mountains?

　　A) It has been hot and dry since thousands of years ago.

　　B) It was warm and damp, and rich in water long time ago.

　　C) It has been transformed by Africans’ agricultural activities.

　　D) It is much the same as it used to be thousands of years ago.

　　50. What’s the significance of scientists’ study results?

　　A) Gaining insight into ancient Africans’ architectures.

　　B) Defining the benefits of changing eating habits.

　　C) Finding the root causes behind the formation of the Sahara Desert.

　　D) Providing the evidence for the effects of global warming.