How can this be built into Salesforce?

Universal Container sells sports shoes through on eCommerce system. The Loyalty Program Members earn points in real-time with every purchase made.

How can this be built into Salesforce?
A . Download an app from the AppExchange to connect Salesforce and the external system.
B . Create customer web service with Order Object
C . Create an schedule process to call the external system.
D . Create with the external system to create Transaction Journals.

Answer: D