数据流图用于抽象描述一个软件的逻辑模型，数据流图由一些特定的图符构成。下列图符名标识的图符不属于数据流图合法图符的是( )。
A．控制流
B．加工
C．数据存储
D．源和潭
参考答案：A
解析：数据流图包括4个方面，即加工(转换)(输入数据经加工变换产生输出)、数据流(沿箭头方向传送数据的通道，一般在旁边标注数据流名)、存储文件(数据源)(表示处理过程中存放各种数据的文件)、源和潭(表示系统和环境的接口，属系统之外的实体)。不包括选项中的控制流。
| 阅读理解。 |
| Nuclear radiation from power plant leaks and bomb tests resulted in millions of fewer baby girls born worldwide, according to a new study. Scientists noted these types of atmospheric blasts rather than ontheground incidents like Chernobyl (切尔诺贝利), effected birth gender across the globe. Scientists at Helmholtz Zentrum M?nchen, Germany, analysed population data from 1975 to 2007 for the U．S. and 39 European countries. There was an increase in the number of baby boys relative to girls in all of the countries from 1964 to 1975. This was the case in many eastern European countries for several years after 1986. Scientists are putting the first spike down to the atomic bomb tests of the 1960s and 1970s where radioactive atoms were blasted into the atmosphere. Air currents caught these atoms and then distributed them around the world. They think the second spike is due to the 1986 Chernobyl disaster in which the reactor exploded in the Ukraine(乌克兰)． The effects of Chernobyl were felt locally and no effect was seen in the U．S., probably because it was too far from the disaster to have an effect. "The closer the country was to Chernobyl, the stronger the effect," said study coauthor Hagen Scherb, a biostatistician(生物统计学家) at the German Research Center for Environmental Health in Munich. More males were born relative to females in Belarus-the Ukraine's neighbour-than in France. The study is based largely on Cold Warera statistics, but the findings are highly relevant for how gender could be affected after future nuclear disasters. And in the wake of Japan's Fukushima Daiichi nuclear power plant accident experts are predicting another baby boy boom could come, especially on the U．S. West Coast. Previous radiation experiments on animals may give a clue for the increase in male births. Tests showed that radiation caused damage to the X chromosome(染色体) in sperm, Dr Scherb said. A human sperm cell contains either an X or Y chromosome, while an egg only has an X chromosome. An XY combination will become a boy, while an XX combination will be a girl. |
| 1．How many nuclear radiation accidents are mentioned in the passage? |
| A．1. B．2. C．3. D．4. |
| 2．Which of the following is true according to the passage? |
| A．The ontheground incidents like Chernobyl, effected birth gender across the globe. B．There was an increase in the number of baby boys in many eastern European countries for several years after 1986. C．The Japan's nuclear accident will not effect the birth gender of the U．S. because of the long distance. D．Where radioactive material has spread, women can't give birth to children. |
| 3．How does radiation effect birth gender? |
| A．It damages the Y chromosome in sperm. B．It stops X chromosomes and Y chromosomes combining. C．It kills baby girls before they are born. D．It damages the X chromosome in sperm. |
| 4．What does the passage mainly tell us? |
| A．Nuclear age has led to millions of fewer baby girls being born. B．Nuclear radiation has bad effects upon people's health. C．Worries about radiation risks. D．Nuclear age helps reduce the world population. |