premise: Mercotek carried out a study to compare the productivity of its night shift with that of its day shift. Every week the company's six crews—F, G, H, R, S, and T—were ranked from first (most productive) to sixth (least productive). There were no ties. For any given week, either G and T were the two night-shift crews or else S and H were—the four other crews were the day-shift crews for that week. The following relationships held for every week of the study: F is more productive than G. R is more productive than S. R is more productive than T. S is more productive than H. G is more productive than T. Which one of the following is a complete and accurate list of the crews that CANNOT be ranked third for any given week of the study?
hypothesis: G, H, S