A. It is a pseudo filesystem that maps processes and kernel data structures to corresponding files.
B. It is a JFS mounted filesystem that provides an exact representation of what is happening to a proces at a single and discrete point of time.
C. It is a JFS mounted filesystem that maps processes and read-only files related to these processes.
D. It is a pseudo filesystem that contains data that represents the state of the parent processes （but not their threads） in a system.