In the second half of each year, many powerful storms are born in the tropical Atlantic and Caribbean seas. Of (91) , only about half a dozen (92) the p, circling winds of 75 miles per hour or more that give them hurricane status, and several usually (93) their way to the coast. There cause millions of dollars of (94) , and bring death to (95) numbers of people.
The great storms that hit the coast start (96) innocent circling disturbances hundreds, even thousands of miles out to sea. As they travel aimlessly over water (97) by the summer sun, they are carried westward by the (98) winds. When conditions are just (99) , warm, moist air flows in (100) the bottom of such a disturbance, moves upward through it and comes out at the top. In the (101) , the moisture in this warm air produces rain, and with it the heat is converted to energy in the form of p winds. As the heat increases, the (102) hurricane begins to swirl in a counter-clockwise motion.
The average life of a hurricane is only about nine days, but it contains almost (103) power than we can imagine. The energy in the heat released by a hurricane’s rainfall in a(n) (104) day would (105) the entire electrical needs of the United States for more than six months. Water, not wind, is the main (106) of death and destruction in a hurricane. A(n) (107) hurricane brings 6-to 12-inch downpours (108) in sudden floods. (109) is the powerful movement of the sea-the mountains of water moving toward the low-pressure hurricane center. The water level (110) as much as 15 feet above normal as it moves toward shore.
A．they
B．these
C．it
D．this
时（T为交流的周期），原线圈中的电流瞬时值为0.03A．变压器的原、副线圈的匝数比为（ ）
：3