Which of the following statements regarding determination letters for qualified plans is true?

a. Employers must request a determination letter from the IRS for all qualified plans.

b. Employers must request a determination letter from the DOL for all qualified plans that are materially modified or materially amended.

c. Employers who receive a favorable determination letter are protected from the IRS disqualifying their qualified plan.

d. Employers must follow each and every aspect of their qualified plan document.