普通小麦中有高杆抗病（TTRR）和矮杆易感病（ttrr）两个品种，控制两对相对性状的基因分别位于两对同源染色体上．实验小组利用不同的方法进行了如下三组实验，下列关于该实验的说法错误的是（    ）

北京见证了中国历史的沧桑巨变。1949年，居住在北京城的居民可能看到的是（    ）

阅读短文，下列问题

 B

      Bill sells Coca-Cola all over the world. Last week, he returned from the Middle East.   

       A friend asked, "How was your business with the Arabs?" "Too bad," Bill said in a sad voice. Then he explained, "When I got to the Middle East, I was very confident that I would have a good sale as Coca-Cola is well known around the world. However, I had a problem - I don't know how to speak Arabic. So I made some nice posters to help sell Coca-Cola. There are three pictures in each poster. In the first picture, a man is crawling (爬行) through ahot desert sand. He is terribly tired and thirsty. In the second one, the man is drinking our Coca-Cola with a big mouth. In the third one, he is smiling happily. Soon such posters were seen."

      "That's a good idea," said the friend. "Well, it should," Bill answered. "But I didn't know that Arabs usually read from right to left."

推理填空：
如图，已知∠1=∠2，∠B=∠C，可推得AB∥CD．理由如下：
因为∠1=∠2（已知），且∠1=∠4（①理由：____ ）
所以∠2=∠4 （等量代换）
所以CE∥BF （②理由：____ ）
所以∠C =∠3（③理由：____  ）
又因为∠B=∠C（已知），
所以∠3=∠B（等量代换）
所以AB∥CD （④理由：____ ）