如果进栈序列为e1,e2,e3,e4,则可能的出栈序列是______。A.e3,e1

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问题:

如果进栈序列为e1,e2,e3,e4,则可能的出栈序列是______。

A.e3,e1,e4,e2

B.e2,e4,e3,e1

C.e3,e4,e1,e2

D.任意顺序

考点:计算机等级考试VISUALBASIC数据结构与算法
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在“研究平抛物体的运动”的实验中记录的一段轨迹.已知物体是从原点O水平抛出,经测量C点的坐标为(60,45).则平抛物体的初速度v0=______m/s,该物体运动的轨迹为一抛物线,其轨迹方程为______.

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行为活动控制是对建设用地内外的各项活动、生产、生活行为等外部环境影响提出的控制要求,主要包括( )两个方面。

A.交通活动控制和环境保护规定
B.历史保护规定和交通活动控制
C.历史保护规定和环境保护规定
D.公共设施控制和交通活动控制

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制造企业经营战略方案,应以关键目标为中心,进行大胆设想,提出各种创意。可供选择的设想方法主要有()。

A.头脑风暴法

B.盈亏分析法

C.滚动计划法

D.备用计划法

E.德尔菲法

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月球本身并不发光,是太阳光将它照亮的,所以,它的亮面总是朝向太阳。()

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Remember Second Life, the virtual world that was supposed to become almost as important as the first one Now populated by no more than 84,000 avatars at a time, it has turned out to be a prime example of how short-lived Internet fads can be. Yet if many adults seem to have given up on virtual worlds, those that cater to children and teenagers are thriving. Several have even found a way to make money.

In America, nearly 10 million children and teenagers visit virtual worlds regularly, estimates eMarketer, a market researcher-a number the firm expects to increase to 15 million by 2013.As in January, there were 112 virtual worlds designed for under-18s with another 81 in development, according to Engage Digital Media, a market research firm.

All cater to different age groups and tastes. In Club Penguin, the market leader, which was bought by Disney in 2007 for a whopping $ 700 million, primary-school children can take on a penguin persona, fit out their own igloo and play games. Habbo Hotel, a service run from Finland, is a global hangout for teenagers who want to customise their own rooms and meet in public places to attend events. Gala Online, based in Silicon Valley, offers similar activities, but is visited mostly by older teens who are into Manga comics.

Not a hit with advertisers, these online worlds earn most of their money from the sale of virtual goods, such as items to spruce up an avatar or a private room. They are paid for in a private currency, which members earn by participating in various activities, trading items or buying them with real dollars.

This sort of stealth tax seems to work. At Gala Online, users spend more than $1 million per month on virtual items, says Craig Sherman, the firm’s chief executive. Running such a virtual economy is not easy, which is why Gaia has hired a full-time economist to grapple with problems that are well known in the real world, such as inflation and an unequal distribution of wealth.

There are other barriers that could limit the growth of virtual worlds for the young, but the main one is parents. Many do not want their offspring roaming virtual worlds, either because they are too commercial or are thought to be too dangerous. Keeping them safe is one of the biggest running costs, because their sponsors have to employ real people to police their realms.

Youngsters are also a fickle bunch, says Simon Levene of Accel Partners, a venture- capital firm. Just as children move from one toy to another, they readily switch worlds or social networks, often without saying goodbye.

Even so, Debra Aho Williamson, an analyst at eMarketer, believes "these worlds are a training ground for the three-dimensional web". If virtual worlds for adults, which so far have been able to retain only hardcore users, manage to hang on for a few years, they may yet have a second life.

Which of the following may NOT be the barriers to limit the growth of virtual worlds()

A.Inflation and unequal distributions of wealth can also happen in the virtual world

B. The virtual world could grow complicated enough to force employment of special staff to manage it

C. Parents would keep their children from the online games in order to keep them safe

D. The online game companies will have to keep the virtual world safe, at some rather high cost

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