如果函数f（x）=2x2-4（1-a）x+1在区间[3，+∞）上是增函数，则实数

近些年，许多发展中国家放弃了种粮，基本依赖国际粮食市场。这种情况的起源是过去数十年间，发达国家以援助为杠杆，向穷国推销“自由市场”的粮食政策：发展中国家向发达国家购买粮食，转而生产经济作物。这一政策推行的结果是：发达国家为自己的农产品打开了市场，而穷国却失去了粮食的自给自足能力。这一事实表明，解决粮食安全问题需要

①发达国家提供资金和技术支持         ②发展中国家减少粮食的消费量

③推动农产品国际贸易环境的改善       ④发展中国家独立自主、自力更生

A．①②

B．③④

C．②③

D．①④

景区内商家：这几个月的营业额明显减少，主要是由于景区门票大幅涨价造成的。景区管理部门：商家的营业额减少和景区门票涨价没有关系，经过我们的调查，商家营业额减少的主要原因，是他们没有采取薄利多销的营销策略。 以下___项如果为真，最能削弱景区管理部门的解释。

A.该景区的门票价格和别的景区相比并不算高 

B.景区管理部门在引导商家进行薄利多销方面做了一些工作，但是力度不够 

C.过高的景区门票价格导致游客数量锐减 

D.商家的营业额减少这一情况再别的景区也普遍存在

下列关于"骨瘤"的描述中，哪项错误（）

A.多见于颅骨外板

B.菜花状，顶端可有不规则钙化

C.可发生于鼻窦内

D.均匀一致高密度

E.多数肿瘤体积不大

Many people are surprised when they find the Internet(因特网)was set up in the 1960s. At that time, computers were large and expensive. Computer networks(网络) didn’t work well. If one computer in the network broke down, then the whole network stopped. So a new network system (系统) had to be set up. It should be good enough to be used by many different computers. If a part of the network was not working, information could be sent through another part. In this way computer network system would keep on working all the time.
At first the Internet was only used by the government, but in the early 1970s,universities(大学) ,hospitals and banks were allowed(允许) to use it too. However, computers were still very expensive and the Internet was difficult to use. By the start of the 1990s, computers became cheaper and easier to use.
Today it is easy to get on-line(上网) and it is said that millions of people use the Internet every day. Sending e-mail is more and more popular among students.
The Internet has now become one of the most important parts of people’s life.

Computers become cheaper and easier to use in the ______.

A. 1960s


B. 1970s

C. 1990s

止血带止血要每隔多久放松一次？（）

A、50分钟

B、10分钟

C、90分钟

D、30分钟