云南普通专升本考试，只超出分数线三分有可能被录...

下列命题中正确的为（）

A.若xo为f(x)的极值点，则必有，f'(xo)=0
B.若f'(xo)=0，则点xo必为f(x)的极值点
C.若f'(xo)≠0，则点xo必定不为f(x)的极值点
D.若f(x)在点xo处可导，且点xo为f(x)的极值点，则必有f'(xo)=0

There Pictures from outer space now show us how much land has changed on earth．These images are taken by Landsat 7,a government satellite．The satellites have been used for 27 years．They reveal the clear-cutting of forests in the northwestern part of the United States．Pictures show the loss of rain forests in South America.
NASA's Darrel Williams speaks about the Landsat 7 Project．He said that an eruption caused trees to burn up in a large forest．Fifteen years later,pinkish images from space show that the trees and plant life are growing again．Williams says that clear-cut areas easily show up in the pictures．He wants Americans to look at how much land is being cleared of forests in our country.
Satellites have provided other information about changes on earth．In the past ten years,more than four miles have shrunk from glaciers in Alaska．Landsat 7 received these computer images of Glacier Bay in Alaska.
Hurricanes Floyd and Irene have damaged the coastline in North Carolina．Runoff from farms and silt have gone into the．ocean according to satellite images．Loss of trees and forests have caused hotter summers in southern cities such as Atlanta,Georgia.
The Landsat 7 images are like pictures in a photo album．Instead of pictures of the family,the album shows changes around the globe in the past 25 years.
A new satellite,Terra,is going to be launched by NASA soon．It will be more advanced than Landsat 7 and will take important global pictures．Ocean temperatures and energy loss will be provided by Terra daily.

Silt and heavy run-off from farms in North Carolina were caused by__.

A.Hurricanes Irene and Floyd
B.Hurricanes Floyd and Carla
C.an eruption from a volcano
D.deforestation of trees

中国特色社会主义文化，就其主要内容来说

A.同经济体制改革是一致的
B.同政治体制改革是一致的
C.同社会主义精神文明是一致的
D.同社会主义物质文明是一致的