起重机的钢索将重物由地面吊到空中某个高度，其速度图象如图所示，则钢索拉力的功率随时间变化的图象可能是选项中的哪一个？（   ）

起重机的钢索将重物由地面吊到空中某个高度，其速度图象如图所示，则钢索拉力的功率随时间变化的图象可能是选项中的哪一个？（   ）

    Our nearest neighbor is the moon. In the sky,  the moon and the sun seem to be of the same size because the moon is much nearer.
The moon makes the tides—the changes in the level of the sea. The moon and the sun together pull the sea. In some parts of the world,  the difference between "high tide" (when the sea is very near to the land) and " low tide" (when the sea is far away from the land) is very big. This is very important for ships.
    The moon is very different from the Earth. Gravity on the moon is six times weaker than that on the Earth. There isn't any air. During the day, it is very, very hot but at night it is very, very cold. Nothing can live on the moon.
    If the moon goes between the Earth and the sun,  we have an eclipse of the sun(日食) . The moon stops the light from the sun and we have night in the day.
    If the Earth goes between the moon and the sun, we have an eclipse of the moon. The moon goes into the shadow(影子) of the Earth and it disappears for a few minutes.

   On Nov.18th, 1908, three men went up in a balloon. They started early in London. The headman was Auguste Gaudron, and the other two men were Tannar and Maitland. They had a big balloon and they were ready for a long way.
   Soon they heard the sea. They were carrying the usual rope, and it was hanging down from the basket of the balloon. At the end of the rope they had tied a metal box. This could hold water, or it could be empty. So they were able to use the box to change the weight of the balloon. The three people were also carrying some bags of sand.
   After the sun rose, the balloon went higher. It went up to 3,000 metres, and the air was very cold. The water in the balloon became ice. Snow fell past the men's basket, and they could see more snow on the ground. The men tried to throw out some more sand; but it was hard. They tried to break the icy sand with their knives, but it was not easy. The work was slow and they were still falling, so they had to drop some whole bags of sand. One of them fell on an icy lake and made a black hole in the ice.
   At last they pulled the box into the basket. It was still snowing; so they climbed to get away from the snow. They rose to 5,100 metres! Everything became icy. They were very cold and  they decided to land. They came down in Poland　heavily but safely. They had travelled 1,797 kilometres from London!

   On Nov.18th, 1908, three men went up in a balloon. They started early in London. The headman was Auguste Gaudron, and the other two men were Tannar and Maitland. They had a big balloon and they were ready for a long way.
   Soon they heard the sea. They were carrying the usual rope, and it was hanging down from the basket of the balloon. At the end of the rope they had tied a metal box. This could hold water, or it could be empty. So they were able to use the box to change the weight of the balloon. The three people were also carrying some bags of sand.
   After the sun rose, the balloon went higher. It went up to 3,000 metres, and the air was very cold. The water in the balloon became ice. Snow fell past the men's basket, and they could see more snow on the ground. The men tried to throw out some more sand; but it was hard. They tried to break the icy sand with their knives, but it was not easy. The work was slow and they were still falling, so they had to drop some whole bags of sand. One of them fell on an icy lake and made a black hole in the ice.
   At last they pulled the box into the basket. It was still snowing; so they climbed to get away from the snow. They rose to 5,100 metres! Everything became icy. They were very cold and  they decided to land. They came down in Poland　heavily but safely. They had travelled 1,797 kilometres from London!

   On Nov.18th, 1908, three men went up in a balloon. They started early in London. The headman was Auguste Gaudron, and the other two men were Tannar and Maitland. They had a big balloon and they were ready for a long way.
   Soon they heard the sea. They were carrying the usual rope, and it was hanging down from the basket of the balloon. At the end of the rope they had tied a metal box. This could hold water, or it could be empty. So they were able to use the box to change the weight of the balloon. The three people were also carrying some bags of sand.
   After the sun rose, the balloon went higher. It went up to 3,000 metres, and the air was very cold. The water in the balloon became ice. Snow fell past the men's basket, and they could see more snow on the ground. The men tried to throw out some more sand; but it was hard. They tried to break the icy sand with their knives, but it was not easy. The work was slow and they were still falling, so they had to drop some whole bags of sand. One of them fell on an icy lake and made a black hole in the ice.
   At last they pulled the box into the basket. It was still snowing; so they climbed to get away from the snow. They rose to 5,100 metres! Everything became icy. They were very cold and  they decided to land. They came down in Poland　heavily but safely. They had travelled 1,797 kilometres from London!