I actually have two questions, but they are based on the same English subject. <br/><br/>1.) "The length of women's skirts is always changing" or " The length of women's skirts are always changing."<br/><br/>2.) "I am the only one of my relatives who know how to play tennis." or "I am the only one of my relatives who knows how to play tennis." <br/><br/>Any help would be greatly appreciated.