CAPM Practice: Demonstrate an understanding of a project management plan schedule

External dependencies are driven by factors outside the project — in this case, a vendor's delivery schedule. These must be incorporated into the project schedule as constraints or external milestone dates. Failure to account for external dependencies is a common cause of schedule surprises.

**Why not A:** A risk is an uncertain future event. The vendor's delivery date of Day 20 is a known fact, not an uncertainty. Since the delivery date is confirmed, it should be treated as a scheduling constraint or external dependency, not as a risk to be monitored.

**Why not C:** An assumption is something believed to be true without proof for planning purposes. The vendor's delivery date is a stated commitment, not an unverified belief. It represents a concrete scheduling constraint that must be incorporated into the project plan.

**Why not D:** An internal constraint originates from within the project or organization. The vendor delivery date is driven by an external party (the vendor), making it an external dependency rather than an internal project constraint.