They have the same color and texture of hair and the same coloring in their faces. The shape of each hand is very similar. The colors in the water basin are also found in the woman's dress. There is a lot of visual unity in the painting by Richard Estes on page 113. Almost everything in the picture is a similar gray rectangle.
Every surface is hard and cold.
I don't see any examples of the artist deliberately putting things close together to create unity. Noguchi's sculpture on page 54 is unified in that it is literally one piece of material. The alterations made to the stone all move in the same direction, up and down, which echoes the shape of the stone. Return to the artwork that you have investigated independently throughout lessons 1 and 2. If so describe it as things that are close together or things that are similar in appearance.