The Parthenon is an ancient Greek temple built in Athens about 438 B. C. Many people think that the Parthenon is one of the world' s most beautiful buildings. It has a grace and balance that have pleased the eyes of man for centuries.
Architects who have studied the Parthenon know that the Parthenon is a giant optical illusion. An optical illusion is a trick our eyes play on us. All the seemingly straight lines of the Parthenon are actually curves(rounded bends). These curves did not happen by accident. The ancient Greeks,who were fine engineers as well as excellent artists, knew that straight lines can sometimes appear to be curved ! So they designed their columns (stone poles) to look straight.
Try drawing two long parallel(平行)lines on paper. Do they seem to look closer together in the middle than at the ends? A tall column is likely to look narrow halfway up, too. The columns of the Parthenon look as if they stand perfectly straight. Actually, they are slightly bigger in size in the middle and go inward a little at the top. If lines were drawn up along opposite sides of the columns, these lines would meet about one mile above the building.
A platform of three steps forms the base on which the Parthenon rests.These steps have strong horizontal(水平)lines that balance the vertical(竖直)lines of the columns.But the steps are not really level and flat!They curve up in the middle because if they were absolutely straight,,they would appear to curve down.The line of the top step,if continued at both ends,would form a circle with a radius of 3. 5 miles.
When is a curved line not a curved line? When our eyes tell us it is straight!
73.The passage mainly tells us_______.      
A. what two parallel lines look like on paper
B. why a curved line can appear to be straight
C. where the secret of the Parthenon Temple lies
D. when the columns of the Parthenon look curved
74.Which of the following is close in shape with the steps of the platform?
A.                B.           C.       D.
75.What can we infer from the passage?
A. The Parthenon is a famous historic building.
B. The Greeks knew a lot about optical illusions.
C. The ancient Greeks were people of intelligence.
D. Curved lines can meet somewhere above a building.