培育人造仿生血管时，必须先除去仿生血管可能会引起免疫反应的特征，然后才能进行血管移植，否则，人造仿生血管移植到患者体内后，患者血液中的____细胞受到仿生血管中的____物质刺激时会大量增殖分化，其中大多数分化成能分泌抗体的细胞，从而引发免疫排斥反应．

2012年，义乌市城市居民人均可支配收入约为44500元，居全省县级市之首，数字44500用科学记数法可表示为( )

欣赏著名作家巴金在他的作品《海上日出》中对日出状况的描写：“果然，过了一会儿，那里出现了太阳的小半边脸，红是红得很，却没有亮光。”这段文字中，给我们呈现了直线与圆的哪一种位置关系（    ）

如图，电灯的灯丝电阻为2Ω，电池电动势为2V，内阻不计，线圈匝数足够多，其直流电阻为3Ω．先合上电键K，过一段时间突然断开K，则下列说法中正确的是（   ）

    Do you know Chen Yixun? He is a great singer from Hong Kong. He has a lot of beautiful songs, so many people love him. This year Chen Yixun gives concerts (演唱会) in some cities in China. And on November 7 the concert is in Jiaxing.

    Chen Yixun wants to give great concerts, and he does a lot of work for that. First, he practises singing every day. And he always drinks warm water. There are also dances at the concerts, so he needs to practice dancing, too. It's a hard job. Then, he also needs to do exercise like running and swimming. He has to be healthy and strong for the concerts.

    “I have a busy life, but I love it. I enjoy singing and I wish to give great shows to people,” says Chen Yixun. Wish him good luck!