3、In the second half of each year, many powerful storms are born in the tropical Atlantic and Caribbean seas. Of these, only about a half a dozen generate（产生） the strong, circling winds of 75 miles per hour or more that give them hurricane status（状况）, and several usually make their way to the coast. There they cause millions of dollars of damage, and bring death to large numbers of people.
The great storms that hit the coast start as innocent（无害的） circling disturbances（搅动） hundreds---even thousands ---of miles out to sea. As they travel aimlessly over water warmed by the summer sun, they are carried westward by the trade winds. When conditions are just right, warm, moist air flows in at the bottom of such a disturbance, moves upward through it and comes out at the top. In the process, the moisture in this warm air produces rain, and with it the heat that is converted（变换） to energy in the form of strong winds. As the heat increases, the young hurricane begins to swirl（漩涡） in a counter-clockwise（逆时针方向） motion.
The average life of a hurricane is only about nine days, but it contains almost more power than we can imagine. The energy in the heat released by a hurricane’s rainfall in a single day would satisfy the entire electrical needs of the United States for more than six months. Water, not the wind, is the main source of death and destruction(毁灭) in a hurricane. A typical hurricane brings 6-to12-inch downpours resulting in sudden floods. Worst of all is the powerful movement of the sea-the mountains of water moving toward the low-pressure hurricane center. The water level rises as much as 15 feet above normal as it moves toward shore.
44.When is an ordinary tropical storm called a hurricane?
A. When it begins in the Atlantic and Caribbean seas
B. When it hits the coastline
C. When it is more than 75 miles wide
D. When its winds reach 75 miles per hour
45What is the worst thing about hurricanes?
A. the destructive effects of water
B. the heat they release
C. that they last about nine days on the average
D. their strong winds
46The counter-clockwise swirling of the hurricane is brought about by _____.
A. the low-pressure area in the center of the storm
B.the force of waves of water
C. the trade winds
D. the increasing heat
47. Apparently the word downpour means _______.
A. heavy rainfall
B. dangerous waves
C. the process of water to the hurricane center
D. the energy produced by the hurricane