1．A tornado （龙卷风） is a violently turning column of air that is in contact with both the surface of the earth and a cumulonimbus cloud （积雨云）．Tornadoes come in many shapes and sizes，but they are typically in the form of a visible condensation funnel （漏斗）．Most tornadoes have wind speeds less than 177km/h，are about 76meters across，and travel several kilometers before disappearing．The most extreme tornadoes can reach wind speeds of more than 483km/h，stretch more than 3.2km across，and stay on the ground for more than 100km．
Various types of tornadoes include the landspout，multiple vortex tornado，and waterspout．Waterspouts are characterized by a spiraling （螺旋式的上升） funnel-shaped wind current，connecting to a large cumulonimbus cloud．They are generally classified as tornadoes that develop over bodies of water，but there is disagreement over whether to classify them as true tornadoes．These spiraling columns of air frequently develop in tropical areas close to the equator，and are less common at high latitudes．Other tornado-like phenomena that exist in nature include the gustnado，dust devil，fire whirls，and steam devil； downbursts are frequently confused with tornadoes，though their action is dissimilar．
Tornadoes have been observed on every continent except Antarctica．However，the vast majority of tornadoes occur in the Tornado Alley region of the United States，although they can occur nearly anywhere in North America．They also occasionally occur in south-central and eastern Asia，northern and east-central South America，Southern Africa，northwestern and southeast Europe，western and southeastern Australia，and New Zealand．
There are several scales （测量仪） for rating the strength of tornadoes．The Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale．An F0or EF0tornado，the weakest category，damages trees，but not strong structures．An F5or EF5tornado，the strongest category，tears buildings off their foundations and can change the shape of large skyscrapers．The TORRO scale ranges from a T0for extremely weak tornadoes to T11for the most powerful known tornadoes．
63．Which are definitely considered as real tornadoes？A
A．Landspouts．
B．Gustnadoes．
C．Downbursts．
D．Waterspouts．
64．From the passage we can learnB．
A．how tornadoes are generally formed
B．how big an area a tornado might strike
C．where the strongest tornadoes may occur
D．where tornadoes can be properly measured
65．It can be inferred from the passage thatD．
A．a cumulonimbus cloud must be the sign of a tornado
B．the South Pole is likely to be frequently hit by tornadoes
C．spiraling wind currents often develop in the United States
D．the Fujita scale is less advanced than the Enhanced Fujita scale
66．The author writes the passage mainly toC．
A．emphasize the destruction by tornadoes
B．analyze the causes of tornadoes
C．introduce different aspects of tornadoes
D．warn people to avoid tornadoes．
分析 本文是一篇科教类阅读，龙卷风是暴力地将联系接触地球表面和积雨云的空气，龙卷风有许多不同的形状和大小，但他们通常在可见的形式凝结漏斗．本文以此展开谈论，主要介绍了龙卷风的不同方面．
解答 63．答案：A．细节理解题．根据"Various types of tornadoes include the landspout，multiple vortex tornado，and waterspout．Waterspouts are characterized by a spiraling （螺旋式的上升） funnel-shaped wind current，connecting to a large cumulonimbus cloud．They are generally classified as tornadoes that develop over bodies of water，but there is disagreement over whether to classify them as true tornadoes．"可知，各种类型的龙卷风包括陆上龙卷风，多个漩涡龙卷风，和排水口，根据描述可排除排水口龙卷风，故为landspout．故选A．
64．答案：B．细节理解题．A．龙卷风如何形成；B．龙卷风会袭击多大的区域；C．最强的龙卷风会在哪里出现；D．哪里的龙卷风可以被合理测量．根据文章内容可知，ACD均不能从文章中得出，B可以．故选B．
65．答案：D．细节理解题．根据"The Fujita scale rates tornadoes by damage caused and has been replaced in some countries by the updated Enhanced Fujita Scale．"可知，the Fujita scale is less advanced than the Enhanced Fujita scale．故选D．
66．答案：C．主旨大意题．阅读全文，本文主要讲述了龙卷风的不同方面．故选C．
点评 本文是一篇科教类阅读，题目涉及多道细节理解题．词义猜测题．做题时学生应仔细阅读原文，把握文章主要内容，联系文章上下文内容并结合所给选项含义，从中选出正确答案，一定要做到有理有据，切忌胡乱猜测．
