Winter sports tend to be more dangerous than summer sports — they take place mostly outside at the mercy of ice or snow, involving (牵涉) metal edges, extreme speeds and crashes. Skeleton (俯视冰梭), however, stands apart as one of the most difficult and least accessible of all the winter sports. Adam Edelman, Israel's first Olympic skeleton athlete, would like to change that.

    Edelman was the 10th athlete named to the 2018 Israeli Olympic Team. Qualifying for the Olympics in any sport is impressive. But it's more impressive if you qualify for the Olympics after only four years in the sport — and without a coach.

    Edelman was first introduced to skeleton watching the game on television in late 2013. Sports have always been a part of his life. He grew up playing football and was a goalkeeper on the Massachusetts Institute of Technology football team. Ready for a new challenge, he set his sights on the Olympics.

Without a coach, Edelman learned to drive by watching endless hours of YouTube videos and taking more runs than anybody else on the track. “When everybody else would take three runs per day, I would take six to eight.” he recalled.

    Succeeding in skeleton takes a large amount of athletic ability and technical skill, but there's one more element (因素) required, one that can't be taught. “These tracks but built in the middle of nowhere, and it's gray and cold. You haven't seen your family in seven months and you really just want to give up. To continue, it takes tenacity.” Edelman said.

    Edelman is already looking beyond Pyeongchang. The 2022 Olympics could be in his future, but whether he continues to compete or not, he promises to stay in Israeli sports as long as possible-as instructor or as a coach.

某校生物兴趣小组，为了探究某些生态因素在生态系统中的作用，用四个相同鱼缸设计了如下实验，分析并回答下列问题．

（1）如果要研究光照在生态系统中的作用，应选取哪两组实验装置____ ，如果要研究水藻在生态系统中的作用，应选取哪两组实验装置？　____ 

（2）如果选择A和C两组实验装置作为对照实验，能否说明河泥在这个生态系统的作用？____ 说说理由．____ 

（3）如果将B和C两组实验作为对照实验，请你提出一个与此相关的探究问题：____ 

阅读理解

          George Gershwin, born in 1898, was one of America's greatest composers. He published his first song when he was eighteen years old. During the next twenty years he wrote more than five hundred songs.

          Many of Gershwin's songs were first written for musical plays performed in theatres in New York City. These plays were a popular form of entertainment in the 1920s and 1930s. Many of his songs have remained popular as ever. Over the years they have been sung and played in every possible way—from jazz to country.

          In the 1920s there was a debate in the United States about jazz music. Could jazz, some people asked, be considered serious music? In 1924 jazz musician and orchestra leader Paul Whiteman decided to organize a special concert to show that jazz was serious music. Gershwin agreed to compose something for the concert before he realized he had just a few weeks to do it. And in that short time, he composed a piece for piano and orchestra which he called Rhapsody in Blue. Gershwin himself played the piano at the concert. The audience were thrilled when they heard his music. It made him world-famous and showed that jazz music could be both serious and popular.

          In 1928, Gershwin went to Paris. He applied to study composition(作曲)with the well-known musician Nadia Boulanger, but she rejected him. She was afraid that classical study would ruin his jazz-influenced style. While there, Gershwin wrot e An American in Paris. When it was first performed, critics(评论家)were divided over the music. Some called it happy and full of life, to others it was silly and boring. But it quickly became popular in Europe and the United States. It still remains one of his most famous works.

          George Gershwin died in 1937, just days after doctors learned he had brain cancer. He was only thirty-nine years old. Newspapers all over the world reported his death on their front pages. People mourned the loss of the man and all the music he might have still written.