What is an activity that consumes no time or resources and shows only that a dependency exists between two activities called?

Thank you for invitation. My opinion is option B is correct.

Activity is effort in time, if there is no one needed for efforts and there is no time taken by it, it's not activity. So my answer is B (A DUMMY ACTIVITY)

A milestone - A milestone is an activity that has been accomplished already in a project. A milestone does not consume any resources, it is resource or time that has already been used by the project.

Option B is correct one ---------------------------------------

Answer is A Milestone & thanks for the invitation.

My answer is for the option (A)