Answer:
D) credible commitment
Explanation:
This is basically an exclusive supplier agreement since Sparkling Leaves and Stan Motors signed a contract that lasts 15 year, and it states that Sparkling Leaves will provide automobile tools only to Stan Motors and Stan Motors will only purchase the tools they need from Sparkling Leaves.
Such a contract needs a serious and credible commitment between both parties, since it lasts several years and it binds both companies to work together exclusively for that period.