SỞ gd- đt vĩnh phúc trưỜng thpt liễn sơN

It is hard to think of a world without gas or electricity. Both are commonly used for lighting and heating today. We now can instantly flick a lighter or strike a match to make a flame. But it was not long ago that there were no such things as matches or lighters. To make fire, it was necessary to strike a piece of iron on flint for sparks to ignite some tinder. If the tinder was damp, or the flint old, you had to borrow some fire from a neighbor. We do not know exactly when or how people first used fire. Perhaps, many ages ago, they found that sticks would burn if they were dropped into some hole where melted lava from a volcano lay boiling. They brought the lighted sticks back to make their fire in a cave. Or, they may have seen trees catch fire through being struck by lightning, and used the trees to start their own fires.

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Today we take electricity for granted and perhaps we do not realize just how useful this discovery has been. Steam was the first invention that replaced wind power. It was used to drive engines and was passed through pipes and radiators to warm rooms. Petrol mixed with air was the next invention that provided power. Exploded in a cylinder, it drove a motor engine. Beyond these simple and direct uses, those forms have not much adaptability. On the other hand, we make use of electricity in thousands of ways. From the powerful voltages that drive our electric trains to the tiny current needed to work a simple calculator, and from the huge electric magnet in steel works that can lift 10 tons to the tiny electric magnet in a doorbell, all are powered by electricity. An electric current can be made with equal ease (thanh thản) to heat a huge mass of molten (nóng chảy) metal in a furnace(lò nung), or to boil a jug (bình, lọ) for a cup of coffee. Other than atomic energy, which has not as yet been harnessed (khai thác) to the full, electricity is the greatest power in the world. It is flexible, and so adaptable for any task for which it is wanted. It travels so easily and with incredible speed along wires or conductors that it can be supplied instantly over vast distances. To generate electricity, huge turbines or generators must be turned. In Australia they use coal or water to drive this machinery. When dams are built, falling water is used to drive the turbines without polluting the atmosphere with smoke from coal. Atomic power is used in several countries but there is always the fear of an accident. A tragedy once occurred at Chernobyl, in Ukraine, at an atomic power plant used to make electricity. The reactor leaked, which caused many deaths through radiation. Now scientists are examining new ways of creating electricity without harmful effects to the environment. They may harness the tides as they flow in and out of bays. Most importantly, they hope to trap sunlight more efficiently. We do use solar heaters for swimming pools but as yet improvement in the capacity of the solar cells to create more current is necessary. When this happens, electric cars will be viable and the world will rid itself of the toxic gases given off by trucks and cars that burn fossil fuels.

A. harmful effects B. the tides C. scientists D. new ways

In the United States and Canada, it is very important to (56)______ a person directly in the eyes when you are having a conversation (57)______ him or her. If you look down or to the side when the (58)______ person is talking, that person will think that you are not interested in (59)______ he or she is saying. This, (60)______, is not polite. If you look down or to the side when you are talking, it might (61)______ that you are not honest. However, people who are speaking will sometimes look away for (62)______ seconds when they are thinking or (63)______ to find the right word. But they always turn immediately (64)______ to look the listener directly in the eyes. These social "rules" are (65)______ for two men, two women, a man and a woman, or an adult and a child.