广东省的鼎湖山是我国建立的第一个国家级自然保护区，因其完整保存了具有400多年历史的地带性植被——南亚热带季风常绿阔叶林，被中外科学家誉为“北回归线沙漠带上的绿洲”。建立该自然保护区的主要目的是为了保护（  ）

目前，有一种先进的汽车制动装置，可保证车轮在制动时不会被抱死，使车轮仍有一定的滚动，安装了这种防抱死装置的汽车，在紧急刹车时可获得比车轮抱死更大的制动力，从而使刹车距离大大减小，假设汽车安装防抱死装置后刹车制动力恒为F，驾驶员的反应时间为t，汽车的质量为m，刹车前匀速行驶的速度为v，则（   ）

著名史学家斯塔夫里阿诺斯在《全球通史》中说：“新皇帝开始将早先在本国取得辉煌成功的法家学说应用到全中国。他废除了所有的封建国家和王国，将广阔的国土划分为若干行政区，每一行政区都配备一批由中央政府任命，并向中央政府负责的官员。”材料所说的行政管理制度最早出现在

夏天的饮食应该注意饮食的卫生和就餐的规律。（   ）

请认真阅读下列短文，从短文后各题所给的A、B、C、D四个选项中，选出最佳选项。
A
    If you travel by air across the center of Africa or South America, you fly over forests for thousands of kilometers. These great forests are the oceans of trees. There are full of thousands and thousands of different kinds of plants and animals.
    However, the world's forests are getting smaller all the time. We are cutting down the trees because we need wood, and we need more farm land. Some people say that there will not be any forests like these in 20 or 30 years. what will happen if they disappear?
    If we cut down our forests, a lot of plants and animals will disappear from the world. In a lot of places the new farm land will soon look like the old deserts. Crops will not grow there. It will not rain very often, and the weather will get very hot. Perhaps the climate of the world will change. This will be dangerous for everyone in the world. That is why we must take care of our forests.