已知一个口袋装有7个只有颜色不同、其它都相同的球，其中3个白球、4个黑球．
（1）求从中随机取出一个黑球的概率；
（2）若往口袋中再放入x个黑球，且从口袋中随机取出一个白球的概率是$\frac{1}{4}$，求x的值．

    We were standing at the top of a church tower. My father had brought me to this high tower in a small town not far from our home in Rome. I wondered why.
 “Look down, Elsa," Father said. I gathered all my courage and looked down. I saw the square in the center of the village. And I saw several streets leading to the square. "See, my dear," Father said gently. “There is more than one way to the square. Life is like that. If you can't get to the place where you want to go by one road, try another."
    Now I understood why I was there. Earlier that day I had begged my mother to do something about the bad lunches that were served at school. But she refused because she could not believe the lunches were as bad as I said.
    When I turned to Father for help, he would not help. Instead, he brought me to this high tower to give me a lesson. By the time we reached home, I had a plan.
    At school the next day, I poured my lunch soup into a bottle and brought it home. Then I asked our cook to serve it to Mother at dinner. The plan worked perfectly. She tried one spoonful and sputtered. “The cook must have gone mad!” Quickly I told what I had done, and Mother promised that she would take up the matter of lunches at school the next day!
    In the years that followed I often remembered the lesson Father taught me. I began to work as a fashion designer two years ago. I wouldn't stop working until I tried every possible way. Father's wise words always remind me that there is more than one way to the square.

下列各组词语中，没有错别字的一组是 （      ）

指出下列错误，并给出理由
1955年，亚非欧国家首脑在印度尼西亚的万隆举行会议。会议期间，***提出“求同存异”的方针，推动会议取得圆满成功。

①细胞膜     ____     A、控制物质进出

②线粒体     ____     B、细胞的控制中心（含有遗传信息）

③细胞核     ____    C、将化学能转化成细胞能利用的能量（动力车间）

④细胞壁      ____    D、将光能转变成化学能（制造有机物的场所）

⑤叶绿体      ____    E、含有细胞液

⑥液泡       ____    F、保护并支持细胞