The correct option is D Introduction of offset press.
The late nineteenth century saw the introduction of offset press. A press that could print up to 6 colours at a time. Introduction of the electrically operated presses in the twentieth century further accelerated the printing operations. The nineteenth century periodicals carried serialised novels, and a new way of writing novels came into being. During the onset of the Great Depression in the 1930s, the printers started printing paperbacks to sustain purchases.