Facebook's charging for user actions that generate more

Solution

The actions and decisions of users will become more and more critical in determining the success of ads. Alternative "b" is incorrect because all social networking sites will be essential for advertisers. Alternative "c" is incorrect because advances in technology allow for more specific measures of an ad's success, rather than the ads becoming inherently more effective. Alternative "d" is incorrect because Facebook's charging for user actions demonstrates the convergence of real and digital worlds.