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An accurate estimation of where a hurricane will strike is essential in order to reduce loss of life and property. Hurricane Andrew, the most costly hurricane in U.S. history, killed 15 people and caused damage of $35 billion, in today's dollars, in 1992. However, the unnamed : Category 4 2 hurricane which struck southeast Florida in 1926 and killed 243 people would have caused an estimated $77 billion if it had struck today. The reason for this is the explosion in population growth and development along the south-east coast of the U.S. during the last half century.
Hurricanes occur in cycles every few decades, the last intense period in the U.S. being from 1940 to 1969. 'Camille', a Category 5 hurricane of such catastrophic force that it caused over a billion and a half dollars worth of damage at the time and killed 256 people, struck the coast of the Gulf of Mexico in 1969 with winds over 320 km/h. Yet, for the last quarter century, hurricane activity has been relatively mild. Only recently has hurricane activity become more intense.
Scientists do not know the precise reason for the cycles of hurricane activity, but they could be caused by a phenomenon called the 'Atlantic Conveyor'. This is the name given to the gigantic current of water that flows cold from the top of the globe slowly along the Atlantic ocean floor to Antarctica and resurfaces decades later before flowing back north, absorbing heat as it crosses the equator. Since hurricanes derive their energy from the heat of warm water, it is thought that an increase in the speed of the' Conveyor', as it pulls warm water to the north, is an indicator of intensifying hurricane activity.
Q5 .....Hurricanes........ become stronger every few decades.
Can Q5 be correct? The paragraph says only recent hurricanes has become intense, but how can we conclude they have been becoming stronger every few decades? In the past, they were mild, not showing gradual intensity!
Hurricanes don't become progressively stronger every few decades. They become strong, then decrease, then become strong again. Your underlined sentences say exactly that. They occur in cycles.