What scope should be requested when using the Oauth token to meet this requirement?

Universal containers (UC) uses a home-grown employee portal for their employees to collaborate. UC decides to use salesforce ideas to allow the employees to post ideas from the employee portal. When clicking some links in the employee portal, the users should be redirected to salesforce, authenticated, and presented with relevant pages .

What scope should be requested when using the Oauth token to meet this requirement?
A . Web
B. Full
C. API
D. Visualforce

Answer: A