设方程x2-4x-1=0的两个根为x1与x2,则x1x2的值是( ) A.-4

题型:选择题

问题:

设方程x2-4x-1=0的两个根为x1与x2,则x1x2的值是(  )

A.-4

B.-1

C.1

D.0

考点:一元二次方程根与系数的关系
题型:选择题

人类认识从古到今有了巨大的发展,特别是现代科学发展更加迅速,新理论层出不穷,新学科不断出现,新知识爆发式地增加,说明了人类认识在快速发展。例如,“由于战争的需要,古代人设烽火台,用烽火和狼烟为信号传递军情。同样的原因,促使现代人创造了无线电波发报、雷达等科学技术去探测和传递军情。”引号里这段说明  [     ]

A、实践是认识的唯一来源

B、人类的认识总是由浅入深,由低级到高级发展

C、实践是认识发展的动力

D、实践不断给人们的认识活动提供必要的物质手段。

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血液向前流动时对血管壁产生的侧压力叫          。主动脉壁一张一缩的搏动,叫             

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Cape Verde is an African country that contists of 10 main islands and 5 tiny ones. It lies in the Atlantic Ocean, about 400 miles west of Senegal on the African mainland .

Cape Verde has a population of about 329,000 and a total area of 1,557 square miles. Sao Tiago, the largest island , covers 383 square miles. There are no people living on Santa Luzia, the last of the ten larger islands,nor on the five small islands.

Praia,the capital of Cape Verde,is on Sao Tiago.However,the largest city,Mindelo,is on Sao Vicente, the sixth largest island of the group. Portugal(葡萄牙)ruled the islands from the 1460's until 1975,when Cape Verde became independent. Now Cape Verde is a republic with an elected president.

About 70 per cent of the people of Cape Verde have mixed black African and Portuguese (葡萄牙的) blood. The rest of the population are mostly black Africans.

1. If you visit Cape Verde,you will find

A. people only on the ten main islands.

B. about 200 people on every square mile of land.

C. people on all the islands except Santa Luzia.

D. no people on the six smallest islands.

2. Five hundred years ago Cape Verde was

A. a free country.

B. a colony (殖民地).

C. an unknown country.

D. a republic.

3. Three out of ten people living in Cape Verde are of

A. mixed Portuguese and African ancestry (祖先).

B. Portuguese ancestry.

C. either Portuguese or African ancestry.

D. African ancestry.

题型:选择题

同质量的各种物质总能量的比较,正确的是()。

A.碳水化合物>蛋白质

B.蛋白质>脂肪

C.脂肪>碳水化合物

D.碳水化合物>脂肪

题型:选择题

下图表示构成细胞的元素、化合物,a、b、c、d代表不同的小分子物质,A、B、C代表不同的大分子物质,据图分析不正确的是()

A.若物质A是动、植物细胞中均含有的储能物质,则A是脂肪

B.物质b是氨基酸,若某种B分子由n个b分子(平均相对分子质量为m)组成的2条链组成,则该B分子的相对分子质量大约为mn-18(n-2)

C.物质c在人体细胞中共有5种,分子中的含氮碱基不同决定了c的种类不同。

D.物质d是性激素,d和胆固醇、维生素D都属于固醇类物质。

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