Scientific research that involves international collaboration has produced papers of greater influence, as measured by the number of times a paper is cited in subsequent papers, than has research without any collaboration. Papers that result from international collaboration are cited an average of seven times, whereas papers with single authors are cited only three times on average. This difference shows that research projects conducted by international research teams are of greater importance than those conducted by single researchers. Which one of the following is an assumption on which the argument depends? ['International research teams tend to be more generously funded than are single researchers.', 'It is possible to ascertain whether or not a paper is the product of international collaboration by determining the number of citations it has received.', 'The number of citations a paper receives is a measure of the importance of the research it reports.', 'The collaborative efforts of scientists who are citizens of the same country do not produce papers that are as important as papers that are produced by international collaboration.']