阅读下列短文，然后根据短文的内容从每小题的四个选择项中选出最佳的一项。

　　A

　　There was a river with a small town on either side of it. The towns were linked by a bridge.

　　One day，a hole appeared in the bridge. Both towns agreed that the hole should be mended. However，disagreement came up as to who should mend it. Each town thought that it had a better reason for the other to mend the hole. The town on the right bank said that it was at the end of the road，so the left-bank town should mend the hole. The town on the left bank，on the other hand，insisted that all the traffic came to the right-bank town，so it was in their interest to mend the bridge.

　　The quarrel went on and on，and so did the hole. The more it went on，the more the hostility between the two towns grew.

　　One day a man fell into the hole and broke his leg. People from both towns questioned him closely about whether he was walking from the right bank to the left or from the left bank to the right，in order to decide which town should be blamed for the accident. But he could not remember，since he got drunk that night.

　　Some time later，a car was crossing the bridge and broke an axle(轴)because of the hole. Neither town paid any attention to the accident，as the traveler was not going from one to the other，but was merely passing through. The angry traveler got out of the car and asked why the hole was not mended.

　　On hearing the reason，he declared，"I'll buy this hole. Who's the owner？"

　　Both towns at once declared that they owned the hole.

　　"One or the other，whoever owns the hole must prove it."

　　"How shall we prove it？"asked both sides.

　　"That's simple. Only the owner of the hole has the right to mend it. I'll buy the hole from whoever mends the bridge."

　　People from both towns rushed to do the job while the traveler smoked a cigar and his driver changed the axle. They mended the bridge in no time and asked for the money for the hole.

　　"What hole？"The traveler looked surprised."I can't see any hole. I've been looking for a hole for several years now. I'm prepared to pay a good price for it，but there's no hole here. Are you pulling my leg or what？"

　　He got into his car and drove off.

　　51. What did the two towns quarrel about？

　　A. Which of them should mend the hole.

　　B. Whether the hole should be mended.

　　C. Why there was a hole in the bridge.

　　D. When they should mend the hole.

　　52. The man who had fallen into the hole failed to answer any questions because he ______.

　　A. had one of his legs broken

　　B. was busy changing the axle

　　C. had drunk too much wine

　　D. was afraid to blame anybody

　　53. Both towns rushed to mend the hole in order to prove that ______.

　　A. they owned the whole bridge

　　B. they had the right to sell the hole

　　C. they were able to mend the hole

　　D. they could afford to mend the hole

　　54. In"Are you pulling my leg or what？"，the phrase pulling my leg refers to ______.

　　A. trying to stop me

　　B. laughing at me

　　C. putting me in trouble

　　D. making fun of me

　　B

　　Scientists have searched for many years for a method to tell whether a volcano(火山)explosion will be small or large. Now，four scientists say they have discovered something in lava(熔岩)that will help do this. They did the research on Mount Unzen on the southern Japanese island of Kyushu.

　　Mount Unzen exploded in November，1990. Since then，more explosions have killed 43 people and destroyed the homes of more than 2，000 others. The volcano is still active today.

　　The scientists say the lava of the volcano contains high level of an element(成份)，which is a sign of the presence of the lava from deep in the earth，not from the surface. They say it shows that the lava coming directly from inside the earth is connected with huge explosions instead of smaller ones.

　　The scientists examined the lava from 18 explosions of Mount Unzen that took place during many thousands of years. They also studied the lava from other volcanoes in the area that are older than Mount Unzen. The lava studied came from both large and small explosions. The scientists found that large explosions contained more of the element than small ones. The scientists say if they had known this two years earlier，they could have warned the people living in the area near Mount Unzen and saved many lives.

　　55. From the passage we learn that Mount Unzen is the name of ______.

　　A. a huge volcano explosion

　　B. a Japanese island

　　C. an active volcano

　　D. a kind of lava

　　56. The four scientists discovered that the level of the element contained in the lava could tell ______.

　　A. the degree of a volcano explosion

　　B. the place of a possible explosion

　　C. the number of volcano explosions

　　D. the time of a possible explosion

　　57. The research of the four scientists was based on ______.

　　A. the lava that caused explosions

　　B. the presence of the lava from the surface

　　C. the damages caused by the 1990 explosion

　　D. the lava from different explosions in the area