Which Salesforce API should be used to implement this integration?

Northern Trail Outfitters is planning to create a native employee facing mobileapp with the look and feel of Salesforce’s Lighting Experience. The mobile ap needs to integrate with their Salesforce org.

Which Salesforce API should be used to implement this integration?
A . Streaming API
B. REST API
C. Connect REST API
D. User InterfaceAPI

Answer: D