读我国“四大地理区域示意图”和“某二地气温曲线和降水柱状图”，回答

已知空气中的声速为340 m/s，现有几种声波：(1)周期为1/20 s；(2)频率为30 Hz；(3)波长为10 m，它们传播时若遇到宽度均为9.5 m的障碍物，能发生明显衍射现象的是(　　)

材料一  列宁在解决战时共产主义的危机时指出“现在最迫切的就是采取那种能够立刻提高农民生产力的办法。”

-----摘自《青海社会科学》

材料二  1933年，美国政府与农场主签定合同，犁掉小麦、棉花各1000多万英亩，以及玉米900多万英亩。政府购买和屠宰了2300万头牛、600多万头生猪，将其当肥料。

------摘自岳麓书社《世界历史》九年级下册

材料三   1950年6月中央人民政府颁布《中华人民共和国土地改革法》，决定在新解放区进行土地改革。……土地改革的基本内容是没收地主阶级的土地和财产，分配给贫苦农民。

材料四   实行家庭联产承包责任制后，安徽凤阳农民这样唱到：“大包干，就是好，干部群众都想搞。只要搞上三五年，吃陈粮烧陈草。个人集体都能富，国家还要盖仓库。”

-----摘自岳麓书社《中国历史》八年级下册   

阅读理解

    Do you know an outstanding junior high or high school teacher, coach, guidance counselor, librarian，or headmaster? Nominate (提名)that special teacher you'll always remember and give him/her the chance to be recognized in a famous national magazine through "Educators of the Year Contest"!

Prizes

    Cash awards will be given to those from across the country who are given the honor of Educators of the Year. Besides, your winning essays will also be published in our magazine.

Guidelines

    We will only consider essays written by teens, and nominations must be for junior high or high school educators only. Elementary school educators are not suitable.

    Convince us your educator is special. Tell us about his or her style of teaching, his or her role in school activities, and community service. What has your educator done for the entire school, your class, for you or another student? Give examples with specific details. Keep your essay between 200 and 1,000 words. Remember to include the first and last name, position, and school of your educator in your essay.

Don't forget to submit (提交)your essays through our website. You can also read our submission guidelines for more information on this website.

The Deadline

    The deadline for submitting your essays is December 30. Your essays are accepted and will appear in our magazine all over the year. Winners will be made public after the January issue is published.