Lines can be parallel in a Euclidean system of geometry. But the non-Euclidean system of geometry that has the most empirical verification is regarded by several prominent physicists as correctly describing the universe we inhabit. If these physicists are right, in our universe there are no parallel lines. Which one of the following is an assumption that is required by the argument? ['Only physicists who are not prominent doubt the view that the universe is correctly described by the non-Euclidean system of geometry that has the most empirical verification.', 'Most physicists have not doubted the view that the universe is correctly described by the non-Euclidean system of geometry that has the most empirical verification.', 'There are no parallel lines in the non- Euclidean system of geometry that has the most empirical verification.', 'The universe is correctly described by the non- Euclidean system of geometry that has the most empirical verification if prominent physicists maintain that it is.']