It is thought that 200 years ago in Australia there were as many languages as there were tribes, which means about 500-600! Linguists have not found any other language in the world related to those of the Australian tribes. However, after years of study they (49) - to establish that the grammar of the old Australian languages was very complicated, comparable to those of ancient Greek or Latin. Aborigines, the natives of Australia, did not wear any clothes and also slept naked. This was extremely interesting for white ethnographers, who wanted to discover why the aborigines (50) - from cold and did not get ill. After various medical examinations it turned out that the aborigines (51)- an extraordinary blood circulation system. The blood which reached the heart was warm, but the blood flowing through the limbs could be cooled down to 12 degrees Centigrade without any bad consequences for the individual. The arms and legs of the natives (52) - ice-cold, but it was enough for the aborigines to do some exercises in the morning to speed up blood circulation and the (53) - organism worked as normal.49. A. could B. can C. were able D. are able50. A. Don't suffer B. didn't suffer C. wouldn't suffer D. Dosen't suffer 51. A. A developed B. Had been developed C. Have developed D. Had developed 52. A. might seem B. Must seem C. may seem D. Can seem53. A. all B. another C. whole D. other