We’ve used the wind as an energy source for a long time. The Babylonians and Chinese were using wind power to pump water for irrigating crops 4,000 years ago, and sailing boats were around long before that. Wind power was used in the Middle Ages, in Europe, to grind(磨碎) corn, which is where the term “windmill” comes from.
We can use the energy in the wind by building a tall tower, with a large propellor（螺旋桨） on the top. The wind blows the propellor round, which turns a generator to produce electricity. We tend to build many of these towers together, to make a “wind farm” and produce more electricity. The more towers, the more wind, and the larger the propellors, the more electricity we can make. It's only worth building wind farms in places that have strong, steady winds, although boats and caravans（大篷车）increasingly have small wind generators to help keep their batteries charged.
The best places for wind farms are in coastal areas, at the tops of rounded hills, open plains and gaps in mountains — places where the wind is strong and reliable. Some are offshore. To be worthwhile, you need an average wind speed of around 25 km/h. Most wind farms in the UK are in Cornwall or Wales. Isolated places such as farms may have their own wind generators. In California, several “wind farms” supply electricity to homes around Los Angeles.
The propellors are large, to obtain energy from the largest possible volume of air. The blades can be angled to cope with varying wind speeds. Some designs use vertical turbines (垂直涡轮机), which don’t need to be turned to face the wind. The towers are tall, to get the propellors as high as possible, up to where the wind is stronger. This means that the land beneath can still be used for farming. 
66. The first paragraph aims to introduce to us _______.
A. the function of wind power                    B. the source of wind power
C. the nations using wind power                    D. the history of using wind power
67. The best places for building the wind farm are places where _______.
A. boats and caravans can often be seen             B. isolated farms don’t have enough electricity
C. there are less human activities                 D. the wind is strong and reliable
68. We can infer from the passage that _______.
A. wind farms will not take up too much farming land
B. wind farms need no fuel because wind is free
C. the blades can be angled to turn to face the wind wherever it comes from
D. the higher and larger the towers are, the stronger the wind is
69. What can be a suitable title for the passage?
A. Where to build a wind farm.                   B. ABC of the using of wind energy.
C. How to make best use of wind.                  D. Wind energy is the best energy.
70.The underlined sentence in the last paragraph means______________________.
A.The blades can increase wind speeds   
B.The blades can decrease the wind speeds
C.The speed of blades can be changed.
D.The blades can be adjusted to face different wind speeds