D-block (for diffuse) elements consist of the transition metals (group 3-12 on the periodic table) in which the outermost electron shell is the D orbital. D-block elements form at least one stable ion with an incompletely filled electron subshell.
... deep-level stations have closed platforms:
Charing Cross tube station (for the Jubilee Line)
Holborn tube station (for the Aldwych branch of the Piccadilly ...