Which of the following statements is true of the X Window System (see Sidebar 4.4)?

A. The X server is a trusted intermediary and attempts to enforce modularity between X clients in their use of the display resource.

B. An X client always waits for a response to a request before sending the next request to the X server.

C. When a program running on another computer displays its window on your local workstation, that remote computer is considered an X server.

Data From Sidebar 4.4

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Sidebar 4.4 The X Window System The X Window System [Suggestions for Further Reading 4.2.2] is the window system of choice on practically every engineer- ing workstation and many personal computers. It provides a good example of using the client/service organization to achieve modularity. One of the main contributions of the X Window System is that it remedied a defect that had crept into the UNIX sys- tem when displays replaced typewriters: the display and keyboard were the only hard- ware-dependent parts of the UNIX application programming interface. The X Window System allowed display-oriented UNIX applications to be completely independent of the underlying hardware. The X Window System achieved this property by separating the service program that manipulates the display device from the client programs that use the display. The service module provides an interface to manage windows, fonts, mouse cursors, and images. Clients can request services for these resources through high-level operations; for example, clients perform graphics operations in terms of lines, rectangles, curves, and the like. The advantage of this split is that the client programs are device indepen- dent. The addition of a new display type may require a new service implementation, but no application changes are required. Another advantage of a client/service organization is that an application running on one machine can use the display on some other machine. This organization allows, for example, a computing-intensive program to run on a high-performance supercom- puter, while displaying the results on a user's personal computer.