In the Context of the Threaded Cognition Theory, When Does

In the context of the threaded cognition theory, when does a bottleneck develop in the attempt to access consciousness?

A) When, for the moment, one knows what he or she is working with, feeling, and thinking
B) When the spotlight of attention lands on the contents of one's mind
C) When one temporarily attends to information at hand or deemed important
D) When tasks compete for access to the workspace of consciousness