把线段比例 改写成数值比例尺是____，从图上量得A、B两地的距离是5.5厘米，A、B两地的实际距离是____千米．

【实验步骤】

①选取在实验种植区(与大田生产条件基本一致)处于快速生长期的大小、长势一致的甘蔗植株，每隔10天左右定时（每天上午10:00）取样3个茎尖并固定。

②制作茎尖细胞分裂临时装片:切取茎尖→用卡诺溶液固定5〜24h，再转入体积分数为70%的酒精保存→解离→步骤A→用改良苯酚品红染液处理8〜16min→压片。

③制作装片，观察、统计细胞总数及处于分裂中期的细胞数，并计算细胞分裂指数（有丝分裂中期细胞数与细胞总数的比值）。

【实验结果】

请回答下列问题。

某种商品的进价为800元，出售时标价为1200元，后来由于该商品积压，商店准备打折销售，但要保证利润率不低于5%，则至多可打（ ）

    Do you know Stephen Hawking? Stephen Hawking was born on 8 January, 1942 in England.When he was older,he went to Oxford University.Stephen wanted to study maths, but maths was not available(可得到的) at University of Oxford. So he studied physics instead. After three years , he went on to do research at Cambridge University.    ①   After leaving the Institute of Astronomy in 1973 , Stephen came to the Department of Applied Mathematics and Theoretical Physics.

    When he was 21 years old, he caught a serious disease.He had to“walk”in his wheelchair living his life.   ②    He continued to do his research in the field of science and he got his Ph.D. He devoted himself to his scientific research. He continued to explore the universe and travelled around the world to give lectures. In 1988, he wrote the book A Brief History of Time. Readers were pleased and surprised to find that a scientist could write about his work in a way that ordinary people could understand. The book explains how science works , tells the readers how the discoveries work and how they change the world.

    In 2002, Hawking visited China and spoke to university students in China. He told the students about his theories and thoughts on some of the greatest questions,“What is time, how did the universe begin, and what exactly are black holes?”

    Stephen Hawking died on 14 March ,2018.He was one of the greatest scientists in the world.We can learn his exploring spirit from him.