Randomly selected seniors and freshmen from four different schools were surveyed as to whether they preferred baseball or or football. Choose all of the tables that show no association between being a senior and preferring baseball. (this is from map exam)

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.