A．They don’t need conventional signs and symbols.
B．They only require a receiver in communication.
C．The distance between communicators can’t be too long.
D．They are not restricted in time and space.

A．The routine trifles in life should be disregarded.
B．Details should be taken down as many as possible.
C．Activities at work should be primarily recorded.
D．There should be no more than 100 entries.