下图为甲、乙、丙、丁四种限制酶的辨识序列。箭头表示每一种限制酶的特定切割部位，其中哪两种限制酶切割出来的DNA片段末端可以互补?其正确的末端互补序列是（   ）

做了20件上衣和35条裤子，还要做几件上衣才能和裤子配套？

已知在平面直角坐标系中，点A（﹣3，﹣1）、B（﹣2，﹣4）、C（﹣6，﹣5），以原点为位似中心将△ABC缩小，位似比为1：2，则点B的对应点的坐标为____．

    Jackie Chan was born on April 7, 1954, in Hong Kong, China. His parents left mainland China for Hong Kong a short time before he was born. His parents named him “Chan Kong-sang”, which means “born in Hong Kong”. They wanted to celebrate a safe trip to Hong Kong.
    At first, Jackie's family lived in the French Embassy(大使馆).His father was a cook, and his mother was a housekeeper. When Jackie was seven years old, his family moved to Australia. His father got a job in the American Embassy. Later, back in Hong Kong, Jackie's father sent him to the China Drama Academy. Jackie studied and worked 19 hours a day. The students practiced Kong Fu and learned how to do many stunts(特技表演)there.
     When Jackie was 17, he began to do dangerous stunts for films. In the early 1980s, Jackie went to Hollywood, but he wasn't very successful. He went on to make films in Hong Kong and had great success. Finally, in 1995,Jackie Chan became famous in the United States. Today, Jackie Chan has both Chinese and American fans and his films make millions of dollars.

某同学在实验室通过实验对草酸进行如下研究。

【查阅资料】①无水硫酸铜吸水后由白色变为蓝色

②氯化钯(PdCl₂)溶液遇CO产生黑色沉淀

【实验准备】选用下列实验装置(气密性良好，部分固定装置已略去)：

  

【实验探究】检验草酸分解的产物。

实验步骤	实验现象	实验结论及分析
⑴按A→D→B→C连接仪器 ⑵关闭K，点燃A处酒精灯	D中____B中澄清石灰水变浑浊C中产生黑色沉淀，气球鼓起	草酸分解生成了CO2、CO和H2O B中反应的化学方程式是：____ ②C中气球的作用是____