The sudden, dramatic explosion in value of

题目：

The sudden, dramatic explosion in value of online social media sites like Facebook and Twitter is reminiscent of the rise, about 15 years ago, of the online businesses that created the "dotcom bubble. " The Internet was far less widely used than it is today. Still, visionaries saw the potential for the Internet we have today, so virtual companies sprung up and grew like weeds as investors threw money their way. Some, like Google and Amazon, developed an enduring online presence and lasting financial value. But far too many quickly lost value when it became apparent that their rapid growth wasn’t yielding revenue.

So, how much is Facebook’s network of users really worth The potential is clear—when so many people are gathered in one virtual place, offering so much personal information about themselves, they create an unprecedented platform for targeted advertising. Or they would, if they were on the network to shop. When eBay and Amazon suggest products to their customers, they’re talking to people who’ve already proven that they’re interested in buying similar products. People go on Facebook for a variety of reasons-to catch up with old friends, share pictures, make new acquaintances, and talk, sometimes endlessly, about themselves. Whether they’ll appreciate having their virtual conversations interrupted by advertising, targeted or not, remains unclear.

It’s also unclear whether Facebook will actually be able to share information about its users’ browsing habits with advertisers. Complaints about the ineffectiveness of Facebook’s privacy policies have arisen in multiple countries, part of a larger social concern about how private information gets used on line. In December, the Federal Trade Commission issued a proposed framework that, among other things, would permit Facebook users to block advertisers from accessing information about their online interests. If that framework is implemented and widely used by Facebook subscribers, it could seriously impair the site’s value as a potential platform for targeted marketing.

What is clear is that Goldman Sachs has a significant interest in Facebook’s financial value, at least for the short term. Goldman Sachs’ decision to invest heavily in Facebook has had some interesting impacts. For one thing, the investment has allowed Facebook an opportunity to postpone issuing an IPO. That means that, at least for the moment, Facebook doesn’t yet have to disclose its finances or publicly address investor complaints.

Goldman Sachs’ investment also puts the firm in an ideal position to handle Facebook’s IPO when it eventually is issued, perhaps sometime next year. That, of course, has the potential to generate substantial revenues for Goldman Sachs’ clients. Google’s 2004 IPO raised an initial $1.2 billion for the company. After all the propaganda, Facebook’s IPO can hardly be expected to raise less. However, there remains a significant question as to whether Facebook’s potential for generating income is more virtual than real. If it turns out that Facebook can’t live up to its potential for generating advertising revenue, venture capitalists who invest for the long term may get burned.

Companies like Amazon and Facebook earn their money by（）

A. luring more visitors to their sites

B. providing easily accessible services

C. attracting advertisements

D. offering a platform for free conversations