Eight large craters run in a long straight line across a geographical region. Although some of the craters contain rocks that have undergone high-pressure shocks characteristic of meteorites slamming into Earth, these shocks could also have been caused by extreme volcanic events. Because of the linearity of the craters, it is very unlikely that some of them were caused by volcanoes and others were caused by meteorites. Thus, since the craters are all different ages, they were probably caused by volcanic events rather than meteorites. Which one of the following statements, if true, would most strengthen the argument? ['No known natural cause would likely account for eight meteorite craters of different ages forming a straight line.', 'A similar but shorter line of craters that are all the same age is known to have been caused by volcanic activity.', 'No known single meteor shower has created exactly eight impact craters that form a straight line.', 'There is no independent evidence of a volcanic event strong enough to have created the high-pressure shocks that are characteristic of meteorites slamming into Earth.']