单项选择题 助消化的药物应在什么时候服用？（）

单项选择题 Glaciers are large masses of ice on land that show evidence of past or presentmovement. They grow by the gradual transformation of snow into glacier ice.A fresh snowfall is a fluffy mass of loosely packed snowflakes, small delicate iceconstals grown in the atmosphere. As the snow ages on the ground for weeks or months,(5) the crystals shrink and become more compact, and the whole mass becomes squeezedtogether into a more dense form, granular snow. As new snow falls and buries the oldersnow, the layers of granular snow further compact to form. firm, a much denser kind ofsnow, usually a year or more old, which has little pore space. Further burial and slowcementation―a process by which crystals become bound together in a mosaic of(10) intergrown ice crystals―finally produce solid glacial ice. In this process ofrecrystallization, the growth of new crystals at the expense of old ones, the percentage ofair is reduced from about 90 percent for snowflakes to less than 20 percent for glacier ice.The whole process may take as little as a few years, but more likely ten or twenty years orlonger. The snow is usually many meters deep by the time the lower layers art convened(15) into ice. In cold glaciers those formed in the coldest regions of the Earth, the entire mass of iceis at temperatures below the melting point and no free water exists. In temperate glaciers,the ice is at the melting point at every pressure level within the glacier, and free water ispresent as small drops or as larger accumulations in tunnels within or beneath the ice.(20) Formation of a glacier is complete when ice has accumulated to a thickness (and thusweight) sufficient to make it move slowly under pressure, in much the same way that solidrock deep within the Earth can change shape without breaking. Once that point is reached,the ice flows downhill, either as a tongue of ice filling a valley or as thick ice cap thatflows out in directions from the highest central area where the most snow accumulates.The up down leads to the eventual melting of ice. Which of the following does the passage mainly discuss?A．The effect of glaciers on climateB．Damage from glaciersC．Glacier formationD．The location of glaciers

单项选择题 What unusual or unique biological train led to the remarkable diversification andunchallenged success of the ants for ever 50 million years? The answer appears to bethat they were the first group of predatory ensocial insects that both lived and foragedprimarily in the soil and in rotting vegetation on the ground. Eusocial refers to a form(5) of insect society characterized by specialization of tasks and cooperative care of theyoung; it is rare among insects. Richly organized colonies of the land made possibleby eusociality enjoy several key advantages over solitary individuals. Under most circumstances groups of workers arc better able to forage for food anddefend the nest, because they can switch from individual to group response and back(10) again swiftly and according to need. When a food object or nest intruder is too large forone individual to handle, nestmates can be quickly assembled by alarm or recruitmentsignals. Equally important is the fact that the execution of multiple-step tasks isaccomplished in a series-parallel sequence. That is, individual ants can specialize inparticular steps, moving from one object (such as a larva to be fed) to another (a second(15) larva to be fed). They do not need to carry each task to completion from start to finish.for example, to check the larva first, then collect the food, then feed the larva. Hence, ifeach link in the chain has many workers in attendance, a senes directed at any particularobject is less likely to fail. Moreover, ants specializing in particular labor categoriestypically constitute a caste specialized by age or body form. or both. There has bees some(20) documentation of the superiority in performance and net energetic yield of various castesfor their modal tasks, although careful experimental studies are still relatively few.What makes ants unusual in the company of eusocial insects is the fact that they arethe only eusocial predators (predators are animals that capture and feed on other animals)occupying the soil and ground litter. The eusocial termites live in the same places as antsand also have wingless workers, but they feed almost exclusively on dead vegetation. Which of the following questions does the passage primarily answer?A．How do individual ants adapt to specialized tasks?B．What are the differences between social and solitary insects?C．Why are ants predators?D．Why have ants been able to thrive for such a long time?