The passage is mainly about . A. when and where debris flows occur B. the experiments t——青夏教育精英家教网—

64. The passage is mainly about ________.

A. when and where debris flows occur　　　　　　 B. the experiments that scientists conduct

C. the causes of debris flows　　　　　　　　　　　　　 D. the possible ways to predict landslides

63. Which of the following is TRUE according the second notice?

A. Applicants must go to the City of Lethbridge for applications in person.

B. The City of Lethbridge will inform all applicants of their final choice.

C. The 2009 Census is expected to be completed on April 22，2009.

D. Applicants must post their applications before February 17，2009．

Earthquakes and volcanic eruptions usually cause the largest, most disastrous debris (碎石) flows. A great many victims of the earthquake that struck Wenchuan of Sichuan province last year were killed not by the quake itself but by the sudden large amounts of debris that followed.

Most debris flows occur where the soil is composed mainly of sand or colluviums (崩积层). Loose soils made up of bits of sand or colluviums fall apart easily and are main material for fast -moving debris flows.

Scientists have conducted endless experiments to find out how debris flows work. They have learned that the amount and the timing of water entering the soil are crucial (决定性的). Typically, that means debris flows often occur when a long rainy period of many weeks is followed by an intense, brief heavy rain.

More often than not, however, debris flows are started by water, in the form of rain, snow, or river flow. In 1998, heavy rains from Hurricane Mitch unleashed about one million tons of mudslides, burying thousands of people in Central America.

Water flows through the soil until it hits a hard layer of bedrock or clay. There the water builds up, filling the tiny spaces between the soil and rock. That buildup reduces the natural friction (摩擦力) that keeps the rock and soil debris lying on the slope. If conditions are approaching dangerous levels, the slope will then fall down.

Despite what scientist know about the fact, debris flows are still impossible to predict at present because there are many other uncertainties affect the stability of each slope. However, one thing is known: On hillsides where one debris flow has occurred, another will eventually follow. The next debris flow could take days, weeks, or years to happen.

62. What can be inferred from the second notice?

A. Applicants can have a three-week paid leave to do the census.

B. Applicants have to walk around the city to do the census.

C. Senior citizens are impossible to be accepted as applicants.

D. New citizens of Lethbridge will not be considered as applicants.

61. What do we know from the first notice?

A. Residents can either attend the meeting or complete a survey to share their input.

B. The consultation will last almost three months before a draft plan comes out.

C. The final plan is due on April l，2009 for the development of the park.

D. Residents must contact Kristine Hebert to finish the survey before February 6.

60. What’s the purpose of the first notice?

A. To inform residents of a meeting in Lake Ontario Park.