Which of the following statements regarding determination letters for qualified plans is true? a. When a qualified plan is created, the plan sponsor must request a determination letter from the IRS b. An employer who adopts a prototype plan must request a determination letter from the IRS c. If a qualified plan is amended, the plan sponsor must request a determination letter from the Department of Labor d. A qualified plan which receives a favorable determination letter from the IRS may still be disqualified at a later date