【正确答案】 A

【答案解析】[听力原文] Good morning, class. It's a beautiful spring day outside, isn't it? So, it's a perfect day to begin talking about migration. Migration is the main strategy that animals have for avoiding adverse environments and taking advantage of rich environments. Now there are all kinds of migrations, but the most familiar one is the seasonal, latitudinal migration. In the fall, the birds fly south, and in the spring they fly north again. In the southern hemisphere, of course, this works in the opposite direction. This is the way that species have been able to colonize, to use those subpolar resources that are seasonally difficult to access, that are unavailable to many living things for half the year. Another kind of seasonal migration is altitudinal migration, which is where animals move vertically rather than to a different region of the earth. They go up the mountain in the spring and down it in the winter. In regions with irregular climate patterns, some animals are nomadic—that is, they just kind of wander around from one area to another as, for instance, the rains bring fresh plant growth to these different places. Many animals of east Africa do this, wandering around the famous Serengeti Plain to where the grass is greenest. Now most such migrations are undergone in search of food and water, but there are also reproductive migrations, where the purpose is to find a habitat that is safe and secure for the young. Some animals, like our Arctic Tern, travel thousands of kilometers a year, and the most amazing thing is that many of them arrive in very specific places, in almost the same place, year after year. How do animals do that, how do they navigate great distances so accurately—and with just the right timing? Well, the answers seem to be multiple. Some migrants just seem to follow coastlines and mountain ranges and other landmarks—and they either remember them, or they are genetically programmed to recognize them, or more likely a bit of both. Other animals use their other senses to help them get where they're going. Research has revealed that our salmon are able to recognize the fine differences in the composition and concentration of the waters flowing from different sources, so that for the salmon, each little stream has its own unique flavour, and they can follow that flavour all the way up the river to their birthplace. Other migrants have evidently evolved very sophisticated navigation systems that use the sun and the stars, or use day length or polarized light, or even use the Earth's magnetic field, as timers and direction finders. How has the professor organized his presentation of migration? 本段录音前两题选项中重复出现的migration和animal以及seasons，direction表明，录音很可能与动物的迁徙有关，可能涉及季节、方向等因素。选项均为名词短语表明，本题可能考查录音的主题，且与migration(迁徙)有关。教授首先提到为了适应不同的气候而进行的季节性迁移，包括水平迁移和垂直迁移，然后又提到游牧式的迁移以及为了食物、水源或繁殖后代而进行的迁移。由此可知，该录音是按照迁移的目的(功能)去展开对动物迁移的阐述，故答案为A。