The correct answer is: D. A printer driver.
A printer driver is a software program that allows your computer to communicate with a printer. It translates the data from your computer into a format that the printer can understand. Without a printer driver, your computer will not be able to print.
File sharing software is not required for printing. However, it can be useful if you want to share files with other people on your network.
A printer enabler is a software program that allows your computer to print to a printer that is not directly supported by the operating system. It is not required for most printers.
The Apple Garamond font set is a set of fonts that are included with the Mac operating system. It is not required for printing.
Therefore, the correct answer is D. A printer driver.