美国正在实验助推火箭无损回收技术：火箭将飞船推送至一定高度；箭船分离，火箭停止喷火、落向地面；接近地面时，火箭再次消耗燃料、向下喷火，并以2m/s的速度匀速下降，如图所示．匀速下降时，火箭的动能 ____（变小/不变/变大），重力势能 ____ （变小/不变/变大）

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阅读下列短文, 从下面每小题的A、B、C、D四个选项中选出最佳选项。

There are some great women scientists in the world. The world would certainly not be so wonderful without their hard work.

Here is a list of some top women scientists and their achievements.

◆Marie Curie

      Curie was born in Poland on November 7, 1867. She was a pioneer in the field of radioactivity(放射). She was also the first person to win two Nobel Prizes, one in physics and the other in chemistry.

◆Rosalind Elsie Franklin

     Franklin was born on July 25, 1920 in London. She graduated from Cambridge University. She played a great role (角色) in the discovery of the structure(结构)of DNA.

◆Annie Jump Cannon

      Cannon was born on December 11, 1863. She was an American astronomer. She divided more than 500,000 stars into different kinds and discovered more than 300 stars in her life.

◆Sally Kristen Ride    

      Ride was born on May 26, 1951. She was an American astronaut. She was the first American woman to travel into outer space.

◆Grace Murray Hopper

      Hopper was born on December 9, 1906 in New York. She was one of the earliest computer programmers and a leader in the development of computer software.