Salesforce Exam Questions

How would an application developer configure this?

A user can only see the fields A, B, and C on a record of Object X until the Stage field value on the
record changes from New to Working. Once the Stage field value is updated to Working and the
record is saved, the user should be able to see fields A, B, C, and D.
How would an application developer configure this?

A.
Use workflow to change the field-level security

B.
Use validation rules to expose the field

C.
Use multiple Visualforce pages

D.
Use workflow to change the record type