Practice

1. Use the guidelines given above and underline the following passage.

    The air in a living room, an office or a factory should be cool and dry. This makes people more comfortable, and they can then relax more, or work better. In some factories it is also necessary to have extremely clean air, so that dust will not spoil the things that are being made.

    Factories that make microchips for computers must have extremely clean air, because the tiniest speck of dust could spoil a microchip. Scientists have suggested that microchip factories could be set up in space, where there is no air at all.

    Air conditioning is used a great deal in hot climates. But even in cooler countries it is valuable, because the air in a room or a building can become very hot if there are a lot of people in it.

    An air conditioning system works by blowing air over the cooling tubes of a refrigerator. If the air is moist, some of the water vapor that it contains will be lost － it will turn into liquid water and left behind. This is because cool air cannot hold as much moisture as warm air can. The cool, dry air is then blown through filters that remove dust and smoke particles. These filters will also remove many of the smells that can make air unpleasant.

2. Read text1 of Unit 1 and underline the most important information of the story.