Final answer:
The correct answer is option b. The annuity mentioned, involving multiplication of accumulation units and their unit value, refers to a Variable annuity where investments in a separate account determine the return.
Step-by-step explanation:
The type of annuity described in the question, where the annuitant multiplies the number of accumulation units by the unit value of the separate account, is characteristic of a Variable annuity. In a variable annuity, the value of each accumulation unit is tied to the performance of a separate investment account, which can fluctuate over time based on market conditions.
The annuitant's payments go into this separate account, which is invested in a variety of instruments, such as stocks or bonds, leading to a variable return on the investment.