新托福考试备考策略与模拟试题

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《新东方·新托福考试备考策略与模拟试题》特点：36个包含阅读、听力、口语及写作的语言技能训练单元，有效帮助考生科学备考；4套完整的全真强化试题，1,200多道经典测试题目，涵盖新托福考试全部题型，全方位强化应试技能 ；全书结构安排合理，每部分都提供了透彻的题型分析和精辟有效的考试技巧与策略；为考生设置了15周的学习计划，提供大量练习资料；特设进度表格，有利于考生自我监督学习进度；随书配有600分钟录音光盘，模拟真实考场情境，强化训练口语和听力。

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ACIDS AND BASESAcids and bases are substances that form compounds and solutions with an electrical charge. When acids dissolve in water, they donate additional hydrogen ions to the solution. An acid, therefore, is a substance that increases the hydrogen ion concentration of a solution. A base, on the other hand, reduces the hydrogen ion concentration of a solution.The strength of acids and bases is measured by using a numeric scale known as pH, a measurement that represents the number of hydrogen ions in a solution, pH is measured with a pH meter or with paper strips that have color indicators. The pH scale runs from 0 to 14, with the midpoint at 7. A neutral solution, such as pure water, has a pH of 7.0. A pH value of less than 7.0 denotes an acidic solution, and a value above 7.0 denotes a basic, or alkaline, solution. The pH of a solution declines as the concentration of hydrogen ions increases; the lower the number, the more acidic the solution. For example, a solution with a pH of 4.5 is far more acidic than one with a pH of 6.0. The pH for bases, or alkalis, is above 7.0, and the higher the number, the greater the basicity or alkalinity. A pH of 8.5 is more alkaline than a pH of 7.5.The internal pH of most living cells is close to 7.0. Most biological fluids measure within the pH range of 6.0 to 8.0. There are a few exceptions, however, including the strongly acidic digestive juice of the human stomach, which has a pH of about 2.0. The chemical processes of living cells are very sensitive to the concentrations of hydrogenions. Biological fluids resist changes to their pH when acids or bases are introduced because of the presence of buffers, substances that minimize changes in the concentrations of these ions. Buffers in human blood, for example, normally maintain the blood pH very close to 7.4 because a person cannot survive very long if the blood pH drops to 7.0 or rises to 7.8.Acids and bases are used in food preparation and in industrial pro

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Nancy Gallagher，美国资深教育专家，有20余年英语教学与教材编写经验，著有《新托福考试备考策略与模拟试题》、《新托福考试冲刺试题》、《新托福考试核心语法》等畅销备考书籍，深受托福考生欢迎。