What Did Steven Johnson Cite Regarding an Educational Conference During

What did Steven Johnson cite regarding an educational conference during which participants were encouraged to post tweets that were displayed on a screen?

A) The tweets were so distracting that little was accomplished.
B) They had no real impact on the conference.
C) People outside the conference joined the conversation, which extended for weeks after the conference ended.
D) Those who posted tweets did not get as much value out of the conference because of multitasking.