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工件坐标系是机床进行加工时使用的坐标系，它应该与编程坐标系一致
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Exports are either raw materials or manufactured goods. Raw materials are products of the land， such as cotton， timber or rubber. Some raw materials， such as iron ore， come from mines. These raw materials are often exported by the countries that produce them to other countries where they are made into manufactured goods. Some countries produce food for export， for example， meat， sugar， or cereals such as wheat and maize. These countries are agricultural countries. An agricultural country needs fertile land and a good climate. A cold， dry climate is not suitable for agriculture. A country which produces manufactured goods is known as an industrialized country. An industrialized country cannot always produce enough food for its own needs. In this case， it does not export foodstuffs. Instead it has to import them. It relies on exports of manufactured products and pays for imports with the money it earns from the exported goods. An industrialized country usually has to import foodstuffs because,（）.
汽车走合前应检查各部位润滑油、制动液、冷却液的数量和（），根据需要进行添加或更换。
风机传动装置的外露部位以及直通大气的（），必须装设防护罩（网）或采取其他安全设施。
软件技术、通信技术、电子技术、控制与显示技术通常称这四类技术为信息技术“四基元”。
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