Read the passage below and then choose the correct answer A, B, C or D. 

In the second half of each year, many powerful storms are born in the tropical Atlantic and Caribbean seas. Of these, only about half a dozen become the strong, circling winds of 74 miles per hour or more that are called hurricanes, 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 soft circling wind 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 southeast winds. When conditions are just right, warm moist air flows in at the bottom of such a wind, 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 is changed to energy in the form of strong winds. As the heat increases, the young hurricane begins to move counter clockwise motion.

The 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 wind, is the main source of death and destruction in a hurricane. A typical hurricane brings 6 to 12 inches downpour, causing sudden floods. Worst of all is the powerful movement of the sea – the mountains of water moving toward the hurricane center. The water level rises as much as 15 feet above normal as it moves toward shore.

When is an ordinary tropical storm called a hurricane?