Who invented the printing press in the 1440s?

The best explanation of the concept that communication is irreversible is:

a. We spend up to 90% of our time involved in purposeful communication activities. b. Rules governing appropriate or acceptable communication are cast in stone. c. Communication is a complicated process. d. You can't take communication back, even if you tell someone to forget your message.

"Um" is an example of an unfilled pause

Indicate whether the statement is true or false.