What is the appropriate authentication solution?

Universal Containers is building a mobile application that connects to Salesforce for reading and updating data

What is the appropriate authentication solution?
A . Create a mobile Integration user ID whose credentials are stored within the mobile application code.
B . Prompt for the mobile user’s username and Password; utilize the oAuth Username-Password flow to obtain an oAuth token.
C . Redirect to Salesforce via the User-agent oAuth flow to obtain an access token and refresh token.
D . Prompt for the mobile user’s username and password; utilize the Enterprise WSDL login() operation to obtain a session I

Answer: C