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①The sun sets on a field in southern England. When it rises again the following morning, that field has become a huge work of art. A large part of the crop has been pressed into a pattern of circles, squares and other shapes.

②Farmers have reported finding strange circles in their fields for centuries. The earliest mention of a crop circle dates back to the 1500s. A woodcut（木版画）from the time showed a “mowing devil” making a crop circle. Crop circles, however, didn’t get attention until 1980, when a farmer in England, discovered three circles, each about 18 meters across, in his field. The world first began to learn about crop circles.

③By the 1990s, crop circles had become something of a tourist attraction. In 1990 alone, more than 500 circles appeared in Europe. Within the next few years, there were thousands.

④Crop circles can be in many different shapes. Most early crop circles were simple circular designs. But after 1990, the circles changed. Crops can be made to look like just about anything—smiling faces, flowers of even words.

⑤People have long been wondering who or what is creating these crop circles. Possibly the most widely known idea is that crop circles are the work of visitors from other planets. Those who agree with the idea say the circles are either the mark left by landing spacecraft or messages brought from afar for us.

⑥Probably the most scientific opinion says that crop circles are created by vortices（漩涡）. They force the air down to the ground, which presses the crops down. Dr. Terence Meaden, an expert in this field, says when the dust gets caught up in a vortex, it can appear to glow, which may explain the UFO—like glowing lights many people have seen. But no one can explain how the air can create such perfect shaped crop circles in just a few seconds.

1．The writer introduce the topic by ______.

A．telling a story	B．asking a question
C．giving a comparison	D．describing a scene

2．The right order of the statements may be ______.
a.More than 500 circles appeared in Europe.
b.The world first began to learn about crop circles.
c.Farmers reported finding strange circles in their field.
d.The circles changed into anything—smiling faces, flowers or words.

A．a-b-c-d

B．b-c-a-d

C．c-b-a-d

D．c-d-a-b

3．The structure of the passage is ______.

A．	B．
C．	D．

4．The best title of the passage probably is ______.

A．Farmers and Strange Circles	B．Different Shapes of Crop Circles
C．Creators of Crop Circles	D．The Mystery of Crop Circles