Laddering Tasks in a Network Diagram Means

Laddering tasks in a network diagram means

A) one task is completed then the next until the final task is complete.
B) each successive task is higher in cost than its predecessor task.
C) allows the project to be completed in the shortest possible time while making the best use of available resources.
D) the resources have to wait until the predecessor activity is complete to move to the next level in the work breakdown structure.