For over two centuries, no one had been able to make Damascus blades-blades with a distinctive serpentine surface pattern-but a contemporary sword maker may just have rediscovered how. Using iron with trace impurities that precisely matched those present in the iron used in historic Damascus blades, this contemporary sword maker seems to have finally hit on an intricate process by which he can produce a blade indistinguishable from a true Damascus blade. Which of the following, if true, provides the strongest support for the hypothesis that trace impurities in the iron are essential for the production of Damascus blades? ['The iron with which the contemporary sword maker made Damascus blades came from a source of iron that was unknown two centuries ago.', 'Although Damascus blades were renowned for maintaining a sharp edge, the blade made by the contemporary sword maker suggests that they may have maintained their edge less well than blades made using what is now the standard process for making blades.', "Production of Damascus blades by sword makers of the past ceased abruptly after those sword makers' original source of iron became exhausted.", 'Almost all the tools used by the contemporary sword maker were updated versions of tools that were used by sword makers over two centuries ago.']