以下历史文献中，对世界反法西斯同盟建立具有促进作用的是：（）A、《波茨坦公告》 B、

镁是一种常见的金属，化学中经常使用镁的单质及其化合物进行实验。

（1）在试管中放入一小块镁条，加入5mL稀盐酸，我们除了观察到反应剧烈、产生大量气泡外，还能观察到的现象是                        。

（2）向MgO与过量的盐酸反应生成的MgCl₂溶液中滴加浓度比较大的NaOH溶液时，刚开始没有出现白色沉淀〔Mg (OH)₂〕，随着氢氧化钠溶液的加入，逐渐出现白色沉淀。请回答下列问题：

①刚开始没有出现白色沉淀的原因是                     (用化学方程式表示) 。

②生成白色沉淀〔Mg (OH)₂〕的化学方程式为：                   。

秦朝时期，张三和李四是邻居，但双方关系很差，互相仇视。某日，张三到县令处告发，称李四在家偷习《诗》、《书》(秦律规定，有敢偶语《诗》、《书》者，弃市)，要求县令对李四定罪。经县令调查，张三告发之事纯属捏造。根据案情，本案应如何处理？( )

A．张三积极向官府报告可能存在的犯罪，即使错误，亦不构成犯罪

B．张三为泄私愤而诬告李四，构成诬告罪，但因未造成损失，从轻发落

C．张三的行为构成诬告罪，以诬告罪惩处

D．张三的行为构成诬告罪，处以弃市的刑罚

患者，女性，40岁。无意中发现背部肿块，无自觉症状，查：局部皮色不变，肿块触之柔软，呈分叶状，推之可移动，无压痛。该患者最可能的诊断是( )

A．痈

B．背疽

C．血瘤

D．脂瘤

E．肉瘤

股票基金A期初的资产净值为10亿元，期末的资产净值为20亿元，期间买入股票的总成本为30亿元，卖出股票的收入为18亿元，则该股票基金的换手率为（）。

A.200%

B.120%

C.150%

D.160%

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.

What may "stealth tax" in "This sort of stealth tax seems to work" refer to（）

A. Online world promotes transaction without seeing the currencies, thus boosting the consumption

B. Things in the online world do not need to be taxed, and then is cheaper than actual ones

C. Companies have already paid the tax for the players

D. People buy things in the online world in a largely unnoticed way, either by himself or by others