Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.
Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger on the ground and depositing a tiny amount of trail pheromone-a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.
Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Attatexana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.
The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna onto the vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space.The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.
What does the passage mainly discuss?




A.How ants mark and follow a chemical trail.
B.Different species of ants around the world.
C.The information contained in pheromones.
D.The mass migration of ants.

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Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions 24 to 31.
Leonardo da Vinci was born on April 15, 1452, in the small Tuscan town of Vinci, near Florence. Leonardo was the son of a wealthy Florentine public official and a peasant woman. In the mid- 1460s, the family settled in Florence, where Leonardo was given the best education that Florence could offer. He rapidly advanced socially and intellectually. He was handsome, persuasive in conversation and a fine musician and improviser. About in 1466, he apprenticed as a studio boy to Andrea Del Verrocchio. In Verrocchio’s workshop, Leonardo was introduced to many activities, from the painting of altarpieces and panel pictures to the creation of large sculptural projects. In 1472, he was entered in the painter’s guild of Florence, and in 1476, he was still mentioned as Verrocchio’s assistant. In Verrocchio’s Baptism of Christ, the kneeling angel at the left of the painting is by Leonardo.
In 1478, Leonardo became an independent master. His first commission, to paint an altarpiece for the chapel of the Palazzo Vecchino, the Florentine town hall, was never executed. His first large painting, The Adoration of the Magi, left unfinished, was ordered in 1481 for the Monastery of San Donato a Scopeto, Florence. Other works ascribed to his youth are the so-called Benois Madonna, the portrait Ginerva de' Benci, and the unfinished Saint Jerome.
In 1482, Leonardo's career moved into high gear when he entered the service of the duke of Milan, Ludovico Sforza, having written the duke an astonishing letter in which he stated that he could build portable bridges; that he knew the techniques of constructing bombardments and of making cannons; that he could build ships as well as armored vehicles, catapults, and other war machines; and that he could execute sculpture in marble, bronze, and clay. He served as a principal engineer in the duke’s numerous military enterprises and was so active also as an architect. In addition, he assisted the Italian mathematician Luca Pacioli in the celebrated work Divina Proportione.
Evidence indicates that Leonardo had apprentices and pupils in Milan, for whom he probably wrote the various texts later compiled as Treatise on Painting. The most important of his own paintings during the early Milan period was The Virgin of the Rocks, two versions of which exist; he worked on the compositions for a long time, as was his custom, seemingly unwilling to finish what he had begun.
From 1495 to 1496, Leonardo labored on his masterpiece, The Last Super, a mural in the refectory of the Monastery of Santa Maria Delle Grazie, Milan. Unfortunately, his experimental use of oil on dry plaster was technically unsound, and by 1500 its deterioration had begun. Since 1726 attempts have been made, unsuccessfully, to restore it; a concerted restoration and conservation program, making use of the latest technology, was begun in 1977 and is reversing some of the damage. Although much of the original surface is gone, the majesty of the composition and the penetrating characterization of the figures give a fleeting vision of its vanished splendor.
During his long stay in Milan, Leonardo also produced other paintings and drawings, most of which have been lost theater designs, architectural drawings, and models for the dome of Milan Cathedral. His largest commission was for a colossal bronze monument to Francesco Sforza, father of Ludovico, in the courtyard of Castello Sforzesco. In December 1499, however, the Sforza family was driven from Milan by French forces; Leonardo left the statue unfinished and he returned to Florence in 1500.
The pronoun “he” in paragraph 3 refers to .




A.Leonardo da Vinci
B.The duke
C.Sforza
D.Milan