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通过________ 可以把要保密的数据对无权存取的用户隐藏起来,从而自动地对数据提供一定程度的安全保护。

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单项选择题Questions 16 to 20 are based on the following reading passage. Reading comprehension Researchers in the field of psychology have found that one of the best ways to make an important decision, such as choosing a university to attend or a business to invest in, involves the utilization of a decision worksheet. Psychologists who study optimization compare the actual decisions made by people to theoretical ideal decisions to see how similar they are. Proponents (支持者)of the worksheet procedure believe that it will yield optimal, that is, the best decisions. Although there are several variations on the exact format that worksheets can take, they are all similar in their essential aspects. Worksheets require defining the problem in a clear and concise way and then listing all possible solutions to the problem. Next, the pertinent considerations that will be affected by each decision are listed, and the relative importance of each consideration or consequence is determined. Each consideration is assigned a numerical value to reflect its relative importance. A decision is mathematically calculated by adding these values together. The alternative with the highest number of points emerges as the best decision. Since most important problems are multifaceted (多层面的),there are several alternatives to choose from, each with unique advantages and disadvantages. One of the benefits of a pencil and paper decision-making procedure is that it permits people to deal with more variables than their minds can generally comprehend and remember. One the average, people can keep about seven ideas in their minds at once. A worksheet can be especially useful when the decision involves a large number of variables with complex relationships. A realistic example for my college students is the question “What will I do after graduation?” A graduate might seek a position that offers specialized training, pursue an advanced degree, or travel abroad for a year. A decision-making worksheet begins with succinct (简洁的)statement of the problem that will also help to narrow it. It is important to be clear about the distinction between long-range and immediate goals because long-range goals often involve a different decision than short-range ones. Focusing on long-range goals, a graduating student might revise the question above to “What will I do after graduation that will lead to a successful career?” 16 Of the following steps, ______ is the one that occurs before the others in making a decision worksheet. A、listing the consequences of each solution B、calculating a numerical summary of each solution C、writing down all possible solutions D、deciding which consequences are most important