Đề ôn tập ĐGNL ĐHQG TP.HCM năm 2025 - Mã đề 11 - Tiếng Anh

The United Nations (UN), an international organization of countries created to promote world peace and cooperation. The UN was founded after World War II ended in 1945. Its mission is to maintain world peace, develop good relations between countries, promote cooperation in solving the world's problems, and encourage respect for human rights. The UN is an organization of countries that agree to cooperate with one another. It brings together countries that are rich and poor, large and small, and have different social and political systems. Member nations pledge to settle their disputes peacefully, to refrain from using force or the threat of force against other countries, and to refuse help to any country that opposes UN actions. UN membership is open to any country willing to further the UN mission and abide by its rules. Each country, no matter how large or small, has an equal voice and vote. Each country is also expected to pay dues to support the UN. As of 2004 the UN had 191 members, including nearly every country in the world. The UN's influence in world affairs has fluctuated over the years, but the organization gained new prominence beginning in the 1990s. It was awarded the Nobel Peace Prize in 2001. Still, the UN faces constant challenges. It must continually secure the cooperation of its member nations because the organization has little independent power or authority. But getting that support is not always easy. Many nations are reluctant to defer their own authority and follow the dictates of the UN.

1. Glass is a remarkable substance made from the simplest raw materials. It can be colored or colorless, monochrome or polychrome, transparent, translucent, or opaque. It is lightweight, impermeable to liquids, readily cleaned and reused, durable yet fragile, and often very beautiful. Glass can be decorated in multiple ways and its optical properties are exceptional. In all its myriad forms – as table ware, containers, in architecture and design – glass represents a major achievement in the history of technological developments.

2. Since the Bronze Age about 3,000 B.C., glass has been used for making various kinds of objects. It was first made from a mixture of silica, lime and an alkali such as soda or potash, and these remained the basic ingredients of glass until the development of lead glass in the seventeenth century. When heated, the mixture becomes soft and malleable and can be formed by various techniques into a vast array of shapes and sizes. The homogeneous mass thus formed by melting then cools to create glass, but in contrast to most materials formed in this way (metals, for instance), glass lacks the crystalline structure normally associated with solids, and instead retains the random molecular structure of a liquid. In effect, as molten glass cools, it progressively stiffens until rigid, but does so without setting up a network of interlocking crystals customarily associated with that process. This is why glass shatters so easily when dealt a blow. Why glass deteriorates over time, especially when exposed to moisture, and why glassware must be slowly reheated and uniformly cooled after manufacture to release internal stresses induced by uneven cooling.

3. Another unusual feature of glass is the manner in which its viscosity changes as it turns from a cold substance into a hot, ductile liquid. Unlike metals that flow or “freeze” at specific temperatures glass progressively softens as the temperature rises, going through varying stages of malleability until it flows like a thick syrup. Each stage of malleability allows the glass to be manipulated into various forms, by different techniques, and if suddenly cooled the object retains the shape achieved at that point. Glass is thus amenable to a greater number of heat-forming techniques than most other materials.