premise: Six paintings hang next to each other as shown below: Each of the paintings is an oil or else a watercolor. Each oil is directly beside, directly above, or directly below another oil. Each watercolor is directly beside, directly above, or directly below another watercolor. Each painting is a nineteenth-century painting or else a twentieth-century painting. Each painting is directly beside, directly above, or directly below another painting painted in the same century. Painting 2 is a nineteenth-century painting. Painting 3 is an oil. Painting 5 is a twentieth-century painting. If there are exactly three oils and three watercolors, which one of the following must be true?
hypothesis: Painting 4 is a watercolor.