Essayist writing in 2012: At its onset, a new medium is limited to carrying content from the old medium it replaces. We are in that phase with e-books -- today' s e-books take their content from print books. Thus it is too early to understand the e-book as a medium, since it has not yet taken its ultimate form. Which one of the following principles, if valid, most helps to justify the essayist's reasoning? ['One medium can replace another only if it can represent richer and more varied content.', 'The ultimate form that a medium will take depends on available technology.', 'A medium cannot be understood without observing the evolution of its content.', 'No electronic medium can resemble a print medium more than it resembles other electronic media.']