阅读理解。
The Sahara Festival is a celebration of the very recent past. The three-day event is not fixed to the same
dates each year, but generally takes place in November or December. It is well attended by tourists, but even
better attended by locals.
During the opening ceremonies, after the official greetings from the government leaders, people who
attend the festival begin to march smartly before the viewing stands, and white camels transport their riders
across the sands. Horsemen from different nations display their beautiful clothes and their fine horsemanship.
One following another, groups of musicians and dancers from all over the Sahara take their turn to show off
their wonderful traditional culture. Groups of men in blue and yellow play horns and beat drums as they
dance in different designs. On their knees in the sand, a group of women in long dark dresses dance with their
hair: their long, dark, shiny hair is thrown back and forth in the wind to the rhythm of their dance.
The local and visiting Italian dogs are anxious to run after hares. The crowd is on its feet for the camel
races. Camels and riders run far into the distance, and then return to the finish Line in front of the cheering
people.
Towards the evening, there comes the grand finale of the opening day, an extremely exciting horserace.
All the riders run very fast on horseback. Some riders hang off the side of their saddles. Some even ride
upside down-their legs and feet straight up in the air-all at full speed. Others rush down the course together,
men arm in arm, on different horses. On and on they went. So fast and so wonderful!
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1. The Sahara Festival is a festival which _____.
A. has a very long history in North Africa
B. is held in the same place on the same day
C. is attended mainly by the people in the Sahara
D. is celebrated mostly by travelers from different countries
2. Before the races begin, _____ take part in the activities during the opening ceremonies.
A. musicians, dancers, horses and hares
B. camel riders, musicians, dogs and hares
C. horsemen, dancers, camels and dogs
D. musicians, officials, camels and horses
3. The underlined word "finale" in the fourth paragraph most probably means the ______of the opening day.
A. first part
B. middle
C. last part
D. whole
4. This passage mainly tells readers _____.
A. what happens on the opening day of the Sahara Festival
B. how people celebrate during the three-day Sahara Festival
C. what takes place at the closing ceremonies of the Sahara Festival
D. how animals race on the first and the last days of the Sahara Festival
， 
， 
， 因而
，
，
，又因轨道3半径比轨道1半径大，所以卫星在轨道1上线速度较大，角速度也较大，故A、B均错误；根据万有引力定律和牛顿第二定律可知：
，即
，卫星在轨道1上经过Q点时和在轨道2上经过Q点时轨道半径相等，则卫星在Q点时加速度相等，故C错误；根据万有引力定律和牛顿第二定律可知：