Read the reading below carefully, and then complete it with the best option A, B, C or D given below:
Background, in relation to computers, on the screen, the color on which characters are displayed. (1) ______, a white background may be used for black characters. In a windowing environment in which more than one program or document can be available to the user, open but currently inactive (2) ______ are said to be in the background. In the context of operating systems and program execution, background refers to a process, or task, assigned a lower priority in the microprocessor's share of time to tasks other than the task running in the (3) ______.

A background process thus often performs (4) ______ work, such as printing or checking for arriving messages on an electronic mail network, invisibly unless the user requests an update or brings the task to the foreground. (5) ______ Only multitasking operating systems are able to support background processing.

(1) ______, a white background may be used for black characters