2017年，人类第一次直接探测到来自双中子星合并的引力波。根据科学家们复原的过程，在两颗中子星合并前约100s时，它们相距约400km，绕二者连线上的某点每秒转动12圈，将两颗中子星都看作是质量均匀分布的球体，由这些数据、万有引力常量并利用牛顿力学知识，可以估算出这一时刻两颗中子星()
B、质量之和
C、速率之和
D、各自的自转角速度
阅读下面短文，掌握大意，然后从每题所给的A、B、C、D四个选项中选出最佳选项。
Once, there was a beautiful girl who didn ’t like herself, because she was blind, she couldn ’t see anything. In fact, the girl __11__ nobody except her boyfriend, for he was always __12__ to help her. She used to tell her boyfriend, “ __13__ I could see the world, I would marry you. ” One day, someone donated* a pair of __14__ to the girl. When the bandages* came off ，she was able to see __15__ ,including her boyfriend for the __16__ time. He asked her, “Now that you can see the world, will you __17__ me?” The girl looked at her boyfriend and was greatly surprised to see that he was blind, __18__ . She had never expected that, and she would not like to be with a blind husband for the rest of her li fe, so she __19__ to marry him. Her boyfriend left in tears and a few days later wrote a __20__ to her, saying, “My dear, take good care of your eyes. Before they are yours, they were __21__ .” So, this is how the human brain* often works when our status* changes. Only a very few remember __22__ life was like before. And we often ask for more than we need. Life is a gift. Today, before you complain about the __23__ of your food ，think of those who have nothing to __24__. Before you complain about life ，think of some ones who went to heaven* too early. Before you complain about your old __25__ , think of the people who are living in the streets. And when you are ti red and complain about your job, think of those who have no jobs. In a word, enjoy the things you have and don ’t forget your past.