Your project depends on a key deliverable from a vendor you've used several times before with great success. You're counting on the delivery to?

A. constraint ---------------

Thanks for invitation

Agree Option D

Option D is correct choice.

In my opinion - OptionD  Explanation: This is an example of an assumption. You've used this vendor before and not had any problems. You're assuming there will be no problems with this delivery based on your past experience.

Thank you for the invitation

my answer is- constraint

The convenient answer is Option A - Constraint.

This can be the example of both Assumption & Constraint and thanks for the invitation.