The man page for command shows the following syntax: The man page for command shows the following syntax: command [ -a | -b ] Which of the following statements is true regarding this entry?（）

A. Either the -a or flag -b may be used, but not both.
B. If the flag -a is used then the flag -b also must be used.
C. One of the -a or -b flags must be used, but not both at the same time.
D. Both the flags may be used together, but neither are mandatory.