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