Architectual (?) Sketches (from Sketchbook)

Black and white sketch on paper of architectural elements. The sketch features simple line drawings of four tower-like structures. The left two structures have a similar shape, with the one on the left taller and triangular top. The right two structures are different; one with a spherical top and one with a domed top. The background of the sketch is marked with smudges and scattered lines. A small number "20" is written in the bottom-left corner. The sketch is surrounded by a thick white border.