已知椭圆x24+y2=1的左、右顶点分别为M、N,P为椭圆上任意一点,且直线PM

题型:选择题

问题:

已知椭圆
x2
4
+y2=1
的左、右顶点分别为M、N,P为椭圆上任意一点,且直线PM的斜率的取值范围是[
1
2
,2],则直线PN的斜率的取值范围是(  )
A.[
1
8
1
2
]
B.[-
1
2
,-
1
8
]
C.[-8,-2]D.[2,8]
考点:椭圆的性质(顶点、范围、对称性、离心率)
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以下哪一项不属于细胞因子的生物学活性()

A.增强抗感染和细胞杀伤效应

B.促进靶细胞的增殖和分化

C.促进炎症过程,影响细胞代谢

D.促进和抑制其他细胞因子和膜表面分子的表达

E.中和及溶解病毒作用

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干细胞可分为哪几种类型?

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车辆在雪天临时停车时,应开启什么灯?

A.前后雾灯

B.倒车灯

C.前大灯

D.危险报警闪光灯

题型:选择题

(D)

Diana Jacobs thought her family had a workable plan to pay for college for her 21-year-old twin sons: a combination of savings, income, scholarships, and a modest amount of borrowing. Then her husband lost his job, and the plan fell apart.

"I have two kids in college, and I want to say ’come home,’ but at the same time I want to provide them with a good education," says Jacobs.

The Jacobs family did work out a solution: They asked and received more aid form the schools, and each son increased his borrowing to the maximum amount through the federal loan (贷款) program. They will each graduate with $20,000 of debt, but at least they will be able to finish school.

With unemployment rising, financial aid administrators expect to hear more families like the Jacobs. More students are applying for aid, and more families expect to need student loans. College administrators are concerned that they will not have enough aid money to go around.

At the same time, tuition(学费)continues to rise. A report from the National Center for Public Policy and Higher Education found that college tuition and fees increased 439% from 1982 to 2007, while average family income rose just 147%. Student borrowing has more than doubled in the last decade.

"If we go on this way for another 25years, we won’t have an affordable system of higher education," says Patrick M. Callan, president of the center. "The middle class families have been financing it through debt. They will send kids to college whatever it takes, even if that means a huge amount of debt."

Financial aid administrators have been having a hard time as many companies decide that student loans are not profitable enough and have stopped making them. The good news, however, is that federal loans account for about three quarters of student borrowing, and the government says that money will flow uninterrupted.

Financial aid administrators believe that ().

A. more families will face the same problem as the Jacobses

B. the government will receive more letters of complaint

C. college tuition fees will double soon

D. America’s unemployment will fall

题型:选择题

阿富汗战争是以反恐为前提的战争,其本质是捍卫美国价值观。()

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