The correct answer is: D. A graphics board.
A graphics board is a hardware device that allows a computer to display graphics. It is also known as a graphics adapter, video card, or graphics processing unit (GPU). A graphics board is required to enable the PC to emulate a graphics terminal because it provides the necessary hardware and software to display graphics.
A laser printer is a type of printer that uses a laser to create images on paper. It is not required to enable the PC to emulate a graphics terminal because it does not provide the necessary hardware or software to display graphics.
A color monitor is a type of monitor that can display images in color. It is not required to enable the PC to emulate a graphics terminal because it does not provide the necessary hardware or software to display graphics.
Software is a set of instructions that tells a computer what to do. It is not required to enable the PC to emulate a graphics terminal because the hardware and software necessary to do so are provided by the graphics board.
Therefore, the correct answer is: D. A graphics board.