I think it is C, because if I'm right present principal is something that is happening presently? If so, C would be the answer because they "are doing" the exercises right now in context.
Answer:
In contrast to classic formulations, active inference makes a distinction between action as a physical state of the real world and beliefs about (future) action that we will refer to as control states—it is these that constitute a sense of agency.
Explanation:
Historical context can tell us important information about D. The author's purpose.
Run and arrive because an adverb is an action word and a train is arriving which is an action and they were running which is an action
