There are warm tropical regions all over the globe, but only the Indians of the South American rain forests have formed the habit of sleeping in the open air. Long before they made painful acquaintance (相识) with Europeans, they had invented something that was unique on earth: the hammock. Nobody really knows who first had the bright idea of making sleeping in the air the symbol of untroubled rest. The Indians see the hammock as a “gift of heaven (上天)”, something given to them a very long time ago. In it the Indians pass away hot noon hours, napping or chatting. Swinging it to and fro (来回摆动) creates a cooling breath of air and keeps away insects. They work and play in hammocks, are born and die there. Hung like a suspension bridge between heaven and earth, a hammock is dry while the soil is damp and is safe from most wild animals. Hammocks have the advantage over beds in that they are easy to transport and take up very little space when they have been rolled up(卷起) . Indians never go on a journey without their hammocks, not even to their plantations. 76.The word hammock in this passage means _______. A. a suspension cage which can be swung to and fro in the air B. a seat hanging by two ropes from the branch of a tree C. a suspension bridge in the South American rain forests. D. a net hung between two supports and used as a bed. 77. When was the hammock invented and by whom? A. The Indians had invented the hammock long before they came to South America. B. The Indians had invented the hammock long before the Europeans came to South America. C. The Europeans invented the hammock after they made acquaintance with the Indians. D. The Europeans had invented the hammock before they went to South America. 78. Indians swing the hammock to_______. A. pray to heaven for a gift       B. keep away flies, mosquitoes and other insects C. keep away wild animals        D. all asleep quickly 79. According to the passage, hammocks _______. A. cannot be rolled up                B. are difficult to transport C. are never brought to the plantations   D. can be kept dry while the ground is wet 80. The passage is about _______. A. the Indian way of living                      B. tropical regions C. Indians' gift for the Europeans           D. a portable bed