What is the Mobile App Attack Surface?

What is the Mobile App Attack Surface?
A . All the different points where an attacker could get into an app and exfiltrate data.
B. Encryption and checksums, access auditing, and data integrity and operational security controls.
C. The resource connection and authentication, authorization, activity logging, data validation, and encoding
D. The sum of all paths for data and commands into and out of the app

Answer: A