.自古长江三峡雄奇险秀，滔滔江水奔腾直下。北魏著名地理学家、散文家郦道元在其脍炙人口的《三峡》名篇中写道：“或王命急宣，有时朝发白帝，暮到江陵，其间千二百里，虽乘奔御风，不以疾也。”文中所描写船的平均速度约为（     ）

先通读下面的短文，掌握其大意，然后从A、B、C、D四个选项中选择可以填入空白处的最佳答案。

    Henry comes from America．He likes1 a lot．He's visited many2．Last summer,he went to India，a county3a long history.During the trip there，he met something4from his culture(文化)．

    One day,he wanted to visit a palace．He went out of the hotel and5a taxi.When he told the driver and palace's name，the Indian6his head．Henry said

    again and the driver shook his head again．Henry,of course，got7．"Why did you always refuse (拒绝)me?"he shouted．"Please drive me to the palace'"The driver answered"Yes．sir!"and shook his8again．The taxi started and Henry didn't say a word．He9it，and then he said to himself,"I see, 'shaking the head' means'10 'here."

关于植物生长素，达尔文、温特等科学家相继进行了长期的具体研究。小研同学对植物生长素的研究非常有兴趣，并设计了如下的实验：

实验假设：如果胚芽鞘的尖端能产生生长素，则能影响胚芽鞘下端的生长。

实验材料：小麦胚芽鞘、刀片、琼脂薄片若干

实验设计：见实验设计示意图

实验结论：上述实验假设成立。有同学认为实验设计不完善，具体改进是____ 。