What is true about medicare part D (Prescription Drug Coverage)?

1. It is a voluntary benefit
2. persons who do not sign up when eligible will be charged with a late fee
3. a late fee will not be charged if a person maintains 'credible coverage'
4. some beneficiaries will have to pay a higher premium based on income.

a. 1, 2, & 3
b. 1 & 2
c. 1, 2, 4
d. all the above.