The decision between C and D hinges on the extent and nature of the vendor's involvement. If hiring the vendor is simply a means to better prepare the project to realize the savings (by improving project management practices), then it is more about exploiting the opportunity. If, on the other hand, the vendor is directly involved in the opportunity itself, taking a share of the savings or playing a major role in the actual realization of the opportunity, then it would be more of a sharing strategy.
Based on the information provided, it seems that the vendor is being brought in to improve project management techniques, which is more aligned with preparing the project to capture the opportunity (Exploit) rather than sharing the opportunity with the vendor.