Many people like the feeling of the gentle wind in spring. Many like to see the falling leaves dancing in the wind in autumn. But sometimes, when the wind becomes a storm, it can be very destructive(具有破坏性的).
A series of such storms struck the US last month and caused very serious damage and human pain.
Every year, major storms cause many problems around the world. There is nothing people can do to stop these powerful forces of nature. But new techniques are helping scientists to predict(预测) how, when, and where big storms will happen. The more exact scientists’ warnings are, the better people can prepare for the storms.
Predictions are improving. “We’re gotten better over the years, especially the last few years,” says Phil Klotzbach, a scientist at an American university. How is a storm formed? Even if scientists know where a storm will happen, winds can suddenly change, carrying the storm to a new direction. “For a hurricane to happen, conditions have to be just right, ” Klotzbach says.
First, the ocean water needs to be warm enough so that it evaporates and rises into the air. As it rises, the vapor（水蒸气）cools and turns back into liquid. This process gives off heat. This produces energy like an engine that causes winds to increase. It drives the formation(形成) of a hurricane.
If wind speeds reach 40 miles per hour, the system is called a “tropical storm”(热带风暴), and it gets a name. At 75 miles per hour, it becomes a hurricane.
Hurricanes that hit the US start when a thunderstorm forms off the coast of Africa. Storms also develop over tropical waters in other parts of the world.
On average, 60 or 70 storms form off Africa every year. About 10 of them get names. There are usually about six hurricanes. Two tend to be very big, with winds of 115 miles per hour or higher.
The hurricane season lasts from June to November. Ninety percent of all hurricanes hit in August, September, and October.
49. According to the passage, hurricanes usually ____.

A．form off the coast of Africa and America

B．travel at 40 miles per hour and get its name

C．cause sea winds to rise and blow over the sea

D．hit parts of the world in summer and autumn

50. The underlined word “evaporates” probably means “____”.

A．begins to move

B．gets lost

C．becomes hot

D．changes into gas

51. Which of the following about the information of a hurricane is the correct order?
a. The ocean water evaporates and goes into the air.
b. Heat creates energy and causes winds to increase.
c. The vapor cools.
d. The ocean water is warm enough.
e. The vapor changes back into liquid.
f. This course gives out heat.

A．a, d, e, b, c, f

B．a, b, c, f, d, e

C．d, a, c, e, f, b

D．d, a, b, c, e, f

52.According to the passage, the speed of the biggest two hurricanes reaches ____.

A．115 miles per hour	B．110 miles per hour
C．75 miles per hour	D．95 miles per hour

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