Which Is a Richer Communication Channel: Instant-Messaging or Ordinary E-Mail

Multiple Choice

Which is a richer communication channel: instant-messaging or ordinary e-mail?

A) E-mail is richer because it gives the user time to think about the message before responding.
B) Instant-messaging is richer because it travels faster than e-mail.
C) Instant-messaging is richer because it allows a quick back-and-forth flow to clarify misunderstandings.
D) E-mail is richer because it allows a quick back-and-forth flow to clarify misunderstandings.