Herb has $20,000 in an interest-bearing time deposit with the Applebottom Bank and Trust Company. While earning a relatively attractive rate of interest, Herb had to agree to not withdraw any of the funds until the end of a three-year period. Herb's investment represents a(n): A. passbook savings account. B. negotiable order of withdrawal (NOW) account. C. individual deferred earnings account (IDEA). D. certificate of deposit (CD).