- 2018年06月05日18:24 来源：小站整理
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1. Accordingto conventional theory, yawning takes place when people are bored or sleepy andserves the function of increasing alertness by reversing, through deeperbreathing, the drop in blood oxygen levels that are caused by the shallowbreathing that accompanies lack of sleep or boredom.
2. The keyfactor in the success of these countries (along with high literacy, whichcontributed to it) was their ability to adapt to the international division oflabor determined by the early industrializers and to stake out areas ofspecialization in international markets for which they were especially wellsuited.
3. In the second case, pollinators(insects, birds) obtain food from the flowering plant, and the plant has itspollen distributed and seeds dispersed much more efficiently than they would beif they were carried by the wind only.
4. In the green-to yellow lightingconditions of the lowest levels of the forest, yellow and green would be thebrightest colors, but when an animal is signaling, these colors would not bevery visible if the animal was sitting in an area with a yellowish or greenishbackground.
5. In a countercurrent exchange system, the blood vesselscarrying cooled blood from the flippers run close enough to the blood vessels carrying warmblood from the body to pick up some heat from the warmer blood vessels; thus,the heat is transferred from the outgoing to the ingoing vessels before itreaches the flipper itself.
6. American paleontologists David Raup and John Sepkoski,who have studied extinction rates in a number of fossil groups, suggest thatepisodes of increased extinction have recurred periodically, approximatelyevery 26 million years since the mid-Cretaceous period.
7. As amongtribes people, personal relationships and a careful weighing of character havealways been crucial in a mercantile economy with little regulation, where one'sword is one's bond and where informal ties of trust cement together aninternational trade network.
8. The explanation is that the Mayaexcavated depressions, or modified natural depressions, and then plugged upleaks in the karst by plastering the bottoms of the depressions in order tocreate reservoirs, which collected rain from large plastered catchment basinsand stored it for use in the dry season.
9. Inequalitiesof gender have also existed in pastoralist societies, but they seem to havebeen softened by the absence of steep hierarchies of wealth in mostcommunities, and also by the requirement that women acquire most of the skillsof men, including, often, their military skills.
10. Ramsay thenstudied a gas that was present in natural gas deposits and discovered that itwas helium, an element whose presence in the Sun had been noted earlier in thespectrum of sunlight but that had notpreviously been known on Earth.
11. Many complex factors led to the adoption of the neweconomies, not only at Abu Hureyra, but at many other locations such as 'AinGhazal, also in Syria, where goat toe bones showing the telltale marks ofabrasion caused by foot tethering (binding) testify to early herding of domesticstock.