Under the simplified method for calculating the taxable amount for an annuity, which of the following statements is true?

a$.$ The amount paid by the employee into the plan is divided by a number based on the age of the employee $($or the employee and spouse$)$ at the starting date of the annuity.

b$.$ The amount paid for the annuity by the employee is recovered first.

c$.$ The amount paid by the employee for the annuity is divided by a number based on the length of employment.

d$.$ The investment in the annuity is divided by a number based on the age of the older annuitant at the starting date of the annuity when there is more than one annuitant $($a joint and survivor annuity$).$