题目:
物体运动的速度方向、加速度方向与作用在物体上合外力的方向之间的关系是 [ ]
A.速度方向、加速度方向、合外力方向三者总是相同的
B.速度方向可与加速度成任何夹角,但加速度方向总是与合外力的方向相同
C.速度方向总是与合外力方向相同,而加速度方向可能与速度方向相同,也可能不相同
D.速度方向总是与加速度方向相同,而速度方向可能与合外力方向相同,也可能不相同
答案:
答案:B
物体运动的速度方向、加速度方向与作用在物体上合外力的方向之间的关系是 [ ]
A.速度方向、加速度方向、合外力方向三者总是相同的
B.速度方向可与加速度成任何夹角,但加速度方向总是与合外力的方向相同
C.速度方向总是与合外力方向相同,而加速度方向可能与速度方向相同,也可能不相同
D.速度方向总是与加速度方向相同,而速度方向可能与合外力方向相同,也可能不相同
答案:B
已知函数f(x)=log2(x2+1)(x≤0),则f-1(2)=______.
Deputy Agriculture Secretary Kathleen Merrigan sees an epidemic (流行病) sweeping across Americas farmland. It has little to do with the usual challenges, such as flood, rising fuel prices and crop-eating insects. The country's farmers are getting older, and there are fewer people standing in line to take their place. National agricultural census (普查) figures show that the fastest-growing group of farmers is the part over 65. Merrigan is afraid the average age will be even higher when the 2012 statistics are completed.
Merrigan, a former college professor, is making stops at universities across the country in hopes of encouraging more students to think about careers in agriculture. Aside from trying to stop the graying of America's farmers, her work is made tougher by a recent blog posting that put agriculture at No.1 on a list of "useless" college degrees. Top federal agriculture officials are talking about the posting, and it has the attention of agricultural organizations across the country.
“There couldn't be anything that's more incorrect," Merrigan said. "We know that there aren't enough qualified graduates to fill the jobs that are out there in American agriculture.
In addition, a growing world population that some experts predict will require 70% more food production by 2050, she said.
“I truly believe we're at a golden age of agriculture. Global demand is at an all-time record high, and global supplies are at all-time record lows," said Matt Rush, director of the Texas Farm Bureau. "Production costs are going to be valuable enough that younger people are going to have the opportunity to be involved in agriculture”.
The Department of Agriculture has programs aimed at developing more farmers and at increasing interest in locally grown food. The National Young Farmers' Coalition has also been pushing for state and federal policy changes to make it easier for new fermers.
Ryan Best, president of Future Fanners of America, has been living out of a suitcase, traveling the country and visiting with high school students about careers in agriculture. The 21 -year-old Best hopes his message-that this is a new time in agriculture-will motivate the next generation to turn around the statistics.“Never before have we had the innovations (创新)in technology which have led to agriculture in this country being the most efficient it has ever been” he said. “There’s really a place for everybody to fit in”
小题1:What is the new challenge to American agriculture?
A.Fewer and older farmers.
B.Higher fuel prices.
C.More natural disasters.
D.Lower agricultural output.小题2:Why is Merrigan visiting universities across the country?
A.To draw federal agriculture officials' attention
B.To select qualified agriculture graduates.
C.To clarify a recent blog posting.
D.To talk more students into farming careers小题3:According to Matt Rush, American agriculture will provide opportunities for younger people because__________.
A.the government will cover production costs
B.global food supplies will be even lower
C.investment in agriculture will be profitable
D.America will increase its food export小题4:What do the underlined words "to turn around the statistics" in the last paragraph mean?
A.To re-analyze the result of the national census.
B.To increase production.
C.To bring down the average age of farmers.
D.To invest more in agriculture.
在Windows98内置的支持多媒体功能的组件中,能够从模拟视频采集数字视频信号,将数据进行压缩存储到文件中,并对视频信息进行处理的是______。
根据《地区电网调度自动化功能规范》(DL/T550-1994),地区电网调度自动化系统基本指标要求,重要遥测量越定值变化传送至主站≤()s
A、3;
B、5;
C、8;
D、10。
TCP和UDP具有多路复用功能。与此相关的协议头字段是()。
A.源IP地址和目的IP地址
B.目的IP地址和目的端口号
C.源IP地址和源端口号
D.源端口号和目的端口号