Answer: D. A promise in a contract with a customer to transfer a good or service to the customer.
Explanation: A performance obligation is defined as an enforceable promise in a contract with a customer to transfer a good or service to the customer.
The good or service provided is distinct, in the sense that it is separable or separately identifiable, are substantially the same and have the same pattern of transfer. This is important because in order to identify performance obligations in a contract, firms needs to determine whether or not the goods or services are distinct.
Some examples of goods or services promised in a performance obligation includes sale of goods, resale of goods purchased, grants, constructing, manufacturing, or developing an asset on behalf of a customer etc.