23. He is the last person left the office yesterday afternoon.
VI. Read the passage and answer the following questions:
Scientists are now looking for cheaper way to use solar energy to heat air and water. Many
buildings are using solar energy to heat their water now. Solar units on the roofs of buildings
collect the energy and use it to heat water. Although these units are still very expensive, more and
more people are buying solar hot water heaters. Universities and colleges give solar energy
courses where students learn to build their own solar collectors. They are also many books that
explain the construction of solar collectors. In the future, there will be more and more solar
collectors, especially in the sunny desert areas of the world.
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