题型:阅读理解 题类:常考题 难易度:普通
福建省厦门市第一中学2017-2018学年高二下学期英语第二次月考试卷
Some materials are obtained from natural resources that are changed by chemical processes in a laboratory. The resulting artificial materials are synthetic, or human-made.
Plastic is a synthetic substance, obtained from petroleum, a fossil fuel. The molecules(分子)in petroleum are split and then linked into chains. Plastic is an example of a polymer, a material made of repeating patterns of atoms linked together. Most polymers are synthetic. They are made by polymerization, the process of chemically linking many smaller molecules to form a larger molecule that has different physical features. Some polymers, such as proteins, occur naturally.
Plastic is a key component of many products. When heated into an almost-liquid form, plastic can be made into fibers, sheets, or molds(模具). It can be mixed with other elements to remain flexible, or it can harden into a solid. Plastic fibers can be made into clothing or carpeting. Sheets of plastic can be made into plates. Molded plastic can be sued for protective helmets or car bumpers.
Most plastics can be reheated and remolded repeatedly. This feature makes plastic very easy to use. Polymers can be pulled into fine strings or molded into almost any kind of shape. For example, tubes of plastic can be shaped into bottles by different processes. One such process is extrusion blow-molding. Most plastics are also resistant to many chemicals that might harm other materials. This quality is the reason that so many cleaning liquids are packaged in plastic bottles.
Plastics are good insulators that can stop electricity or heat to pass through. Look around your kitchen, and observe where plastics are used. Pot handles are sometimes made of plastic, as are cooking tools, toaster controls, and microwave cookware. Food-storage wraps and containers may be made of plastic. Take a walk outdoors, and note all the plastic items you see. Gardening tools, such as watering cans and sprayers, are often made of plastic. Swings and slides made of plastic do not become as hot as metal, so they are safer for play. Because plastics can be heated, remolded, and made into something else, they can be recycled and reused.
a. Heat the plastic tube.
b. Open the mold and remove the bottle.
c. Blow air into the plastic tube constantly.
d. Open the mold, put the tube in and closes the mold.
e. Let the tube expand to take the shape of the inside of the mold.
I. Reusable.
II. More resistant to chemicals.
III. Safer to produce.
IV. Easier to handle.
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