Tornadoes are nature’s most violent storms, which can cause deaths and destroy a neighborhood in seconds. A tornado appears as a rotating, funnel-shaped (漏斗形的) cloud that extends from a thunderstorm to the ground with whirling winds that can reach 300 miles per hour. Damage paths can be over one mile wide and 50 mileslong. Every state is at some risk from this disaster.
Some tornadoes can be seen clearly, while rain or nearby low-hanging clouds cover others. At many times, tornadoes develop so rapidly that little, if any, advance warning is possible.
Before a tornado hits, the air may become very still. A cloud of debris (散片) can mark the location of a tornado even if a funnel can not be seen. Tornadoes generally occur near the edge of a thunderstorm, when the strong wind may die down. It is not uncommon to see clear, sunlit skies behind a tornado.
The following are facts about tornadoes:
☆The average forward speed of a tornado is 30 MPH, but may vary from still to 70 MPH. Debris is picked up or a cloud forms in the funnel.
☆The average tornado moves southwest to northeast, but tornadoes have been known to move in any direction. Tornadoes are most often reported east of the Rocky Mountains during spring and summer months.
☆Tornadoes can happen together with tropical storms and hurricanes as they move onto land. Waterspouts are tornadoes that form over water.
☆Peak tornado season in the southern states of America is March through May; in the northern states, it is late spring through early summer. Tornadoes are most likely to occur between 3 p.m. and 9 p.m., but can occur at any time.
【小题1】From the passage, we learn that tornadoes come from ______.| A．hurricanes | B．great heat |
| C．thunderstorms | D．sandstorms |
| A．The wind may die down. | B．A clear and sunlit sky may appear. |
| C．The air may become still. | D．Its position may be marked by clouds. |
| A．only happen in the late hours of the day | B．only move from southwest to northeast |
| C．may form over sea water | D．often move at a speed of 70 MPH |
| A．tornadoes warning systems are well-developed in many countries |
| B．of all the natural disasters, tornadoes cause the greatest damage |
| C．tornadoes are mostly seen in the southern states of America |
| D．tornadoes may strike so quickly that there is often little or no warning |
