Today,only 4 million people live and work on farms in the United States,but they produce more than enough food for 200 million Americans.They are able to do this because modern agriculture depends more on up-to-date machinery and scientific methods than it does on old-fashioned knowledge and human labor.
These days,one man or woman spending an afternoon in an air-conditioned,stereo-equipped tractor can do the work that years ago would have required hundreds of hours of back-breaking drudgery.
As a result of the modernization of agriculture,the farm of today looks a lot like a factory.When the farmer's hens lay their eggs,conveyor belts carry the eggs off to be sorted and packed.If the farmer keeps pigs,those pigs will not be wallowing in the mud,but lying around in sanitary pens.And the farmer is likely to be found studying a computer print-out of long-range weather conditions.Why isn’t the farmer milking cows in the barn?The answer is easy:A machine is doing it.
This reliance on modern technology has its problems for farmers.The tractors that plow their fields,the combines that reap and thresh the grain,and the silos that store the grain for winter feeding are all very expensive.For example,a single tractor can cost as much as$50,000.Without this equipment,farmers could not run their farms profitably,but,to pay for it,farmers must take out large bank loans.A single bad season could put them deeply in debt.And,when the machinery wears out or becomes obsolete,the farmers must replace it with newer,more expensive models.Still,most farmers are willing to put up with these difficulties because their machines have freed them from the heavy labor and hard life that farmers had to endure in the past.
The first paragraph suggests that（ ）.
从第一段内容来看，主要是想说明美国的农业已经有了长足的发展。A项内容并无法从文中推出；选项CD项在第一段已有明确说明，不能算推出内容。故本题正确答案选B。
下列关于公司的表述，正确的是（）
以下各项列举了我国常见气象灾害与其发生地区的对应关系，其中正确的一项是（）
根据电视收视率调査，看体育节目的观众中青年人比中老年人要多。
由此可推断出（）
—种海洋蜗牛产生的毒素含有多种蛋白，把其中的一种给老鼠注射后，会使有两星期大或更小的老鼠陷入睡眠状态，而使大一点的老鼠躲藏起来。当老鼠受到突然的严重威胁时，非常小的那些老鼠的反应是呆住，而较大的那些老鼠会逃跑。
以上陈述的事实最有力地支持了以下哪项假说？（）
疾病控制中心对某校髙中三个年级的学生进行抽样做视力状况调查，抽样的方法为分层抽样（按比例抽样），若高中一、二、三年级学生人数分别为626、703、780，样本容量为84，则应从离二年级抽样的学生人数为多少？（）
