正在飞行的A、B两架飞机具有相同的重力势能,且mA>mB,则( ) A.A飞机飞

题型:选择题

问题:

正在飞行的A、B两架飞机具有相同的重力势能,且mA>mB,则(  )

A.A飞机飞得快

B.A飞机飞得慢

C.A飞机飞得高

D.A飞机飞得低

考点:势能大小的比较
题型:选择题

一个三角形的面积是2.5平方分米,底是2.5分米,高是(    )分米。

题型:选择题

Jane warns us that our group is going to be very tired and dirty by the afternoon and she is right. However, the evening makes it all ______.

A. favorable       B. worthwhile     C. precious        D essential

题型:选择题

以下是探究唾液淀粉酶对淀粉的消化作用的过程:①取A、B、C三只试管,分别加入大小相近的等量馒头碎屑,再向A中加入2毫升清水,向B和C中各加入2毫升唾液.②将A、B试管充分搅拌,C试管不搅拌,放入盛有37度的温水中10分钟.③分别向三只试管中滴加碘液,观察颜色变化.分析回答:

(1)A试管______B试管______C试管______.

(2)这个实验中的对照组是______实验组是______.

(3)将馒头撕碎和进行搅拌相当于口腔中______和______.

(4)将试管放在37度温水中的原因是______.

(5)咀嚼饭粒或馒头时会越嚼越甜是因为______.

题型:选择题

防火防爆的技术措施主要有( )几方面。

A.防止可燃可爆系统的形成

B.消除、控制引燃能源

C.隔离与防护

D.采取定向失效模式

E.配备灭火器材

题型:选择题

It’s a cliche—but true—that a huge obstacle to a per economic recovery is the lack of confidence in a p recovery. If consumers and businesses were more confident, they would be spending, hiring and lending more freely. Instead, we’re deluged with reports suggesting that, because the recession was so deep, it will take many years to regain anything like the pre-crisis prosperity. Just last week, for example, the McKinsey Global Institute released a study estimating that the country needs 21 million additional jobs by 2020 to reduce the unemployment rate to 5 percent. The study was skeptical that this would happen. Pessimism and slow growth become a vicious cycle.

Battered confidence most obviously reflects the ferocity and shock of the financial collapse and the ensuing recession, including the devastating housing collapse. But there’s another, less appreciated cause: disillusion with modern economics. Probably without realizing it, most Americans had accepted the fundamental promises of contemporary economics. These were: First, we know enough to prevent another Great Depression; second, although we can’t prevent every recession, we know enough to ensure sustained and, for the most part, p recoveries. These propositions, endorsed by most economists, had worked themselves into society’s belief structure.

Embracing them does not preclude economic disappointments, setbacks, worries or risks. But for most people most of the time, it does preclude economic calamity. People felt protected. If you stop believing them, then you act differently. You begin shielding yourself, as best you can, against circumstances and dangers that you can’t foresee but that you fear are there. You become more cautious. You hesitate more before making a big commitment-buying a home or car, if you’re a consumer; hiring workers, if you’re an employer; starting a new business, if you’re an entrepreneur; or making loans, if you’re a banker. Almost everyone is hunkered down in some way.

One disturbing fact from the McKinsey report is this: The number of new businesses, a traditional source of jobs, was down 23 percent in 9,010 from 2007; the level was the lowest since 1983, when America had about 75 million fewer people. Large corporations are standoffish. They have about $2 trillion of cash and securities on their balance sheets, which could be used for hiring and investing in new products.

It’s not that economics achieved nothing. The emergency measures thrown at the crisis in many countries exceptionally low interest rates, "stimulus" programs of extra spending and tax cuts—probably averted another Depression. But it’s also true that there’s now no consensus among economists as to how to strengthen the recovery. Economists suffer from what one of them calls "the pretense-of-knowledge syndrome." They act as if they understand more than they do and presume that their policies, whether of the left or right, have benefits more predictable than they actually are. It’s worth remembering that the recovery’s present slowdown is occurring despite measures taken to speed it up.

So modern economics has been oversold, and the public is now disbelieving. The disillusion feeds stubbornly low confidence.

Were they more open-minded about economic calamities, people would()

A. take care not to trigger them in the first place

B. become more cautious in making purchase decisions

C. become less hesitant in economic activities

D. feel more protected from unforeseeable dangers

更多题库