A cube is cut by a plane, and the orthogonal projections of the remaining part are shown in the figure on the right. The ratio of the volume of the cut-off part to the volume of the remaining part is
(A) $\frac { 1 } { 8 }$
(B) $\frac { 1 } { 7 }$
(C) $\frac { 1 } { 6 }$
(D) $\frac { 1 } { 5 }$