premise: A store sells shirts only in small, medium, and large sizes, and only in red, yellow, and blue colors. Casey buys exactly three shirts from the store. A shirt type consists of both a size and a color. Casey does not buy two shirts of the same type. Casey does not buy both a small shirt and a large shirt. No small red shirts are available. No large blue shirts are available. If Casey buys exactly one medium shirt and does not buy two shirts of the same color, then she cannot buy which one of the following?
hypothesis: a medium yellow shirt