当年，马克思在图书馆博览群书时有人问他，涉猎那么多门类的知识能用得上吗？马克思反问，你愿意只在自己的一块草地上赏花吗？正因为马克思知晓世界是普遍联系的，所以他才不会安于“在一块草地上赏花”。材料告诉我们（    ）

$\sqrt{\text{9}}$所表示的是 （     ）$$

阅读下列短文，从每题所给的A、B、C和D项中，选出最佳选项。

                                                                              Musicians wanted

      We want four good musicians for our rock band(摇滚乐队). Are you a musician? Can you sing? Can you play the piano, the guitar or the drums? Do you want to be the best musician? If you want to join us, please send(发送) an e-mail. Our e-mail address is rockband2009 @pep.com.cn. Or you can call Mr. Liu at 790-4566.

                                                                             Teachers needed

      Are you an art te acher? Can you paint (绘画) or draw well? Are you good with kids? We need two teachers for our art club. Please find Mrs Wang for more information(信息) or call 628-1183.

安装实验装置过程中，斜槽末端的切线必须是水平的，这样做的目的是（　　）