Even though trading in ivory has been outlawed by international agreement, some piano makers still use ivory, often obtained illegally, to cover piano keys. Recently, experts have devised a synthetic ivory that, unlike earlier ivory substitutes, has found favor with concert pianists throughout the world. But because piano makers have never been major consumers of ivory, the development of the synthetic ivory will ttherefore probably do little to help curb the killing of elephants, from whose tusks most natural ivory is obtained. Which one of the following, if true, most helps to strengthen the argument? ['The most common use for natural ivory is in ornamental carvings, which are prized not only for the quality of their workmanship but also for the authenticity of their materials.', 'The new synthetic ivory can be manufactured to resemble in color and surface texture any of the various types of natural ivory that have commercial uses.', 'Most people who play the piano but are not concert pianists can nonetheless easily distinguish between the new synthetic ivory and inferior ivory substitutes.', 'It costs significantly less to produce the new synthetic ivory then it does to produce any of the ivory substitutes that scientists had developed previously.']