问题详情：
The History of Air Conditioners
The first practical cooling system for use in industry 6 1 (invent) in 1902 by Willis
Carrier in New York, the USA. He continued to improve 62 （he) invention and, in 1928,
developed the first air conditioner for home use. In 1939, an American car company
introduced the first air conditioner for cars, 63 (make) driving more comfortable.
After World War II many American 64 (company) began making air conditioners
and, beginning in 1950, many homes in the USA were equipped 65 central air
conditioning. Central air conditioning uses a single unit 66 （heat) or cool a whole house.
With this, people could escape the heat of summer and the cold of winter no matter 67
they were in the house.
In the 1970s, electricity 68 （become) more expensive, so people developed 69
(good) air conditioners to save money. Later, the cooling gas in air conditioners was found to
pollute the environment, so engineers have been working to produce air conditioners more
friendly to the environment 70 the 1980s.
【回答】
61. was invented 62. his 63. making 64. companies
65. with 66. to heat 67. where 68. became 69. better 70. since
知识点：语法填空
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