With constant tax rates over time, why does a single premium deferred annuity contract (SPDA) provide greater

Question:

With constant tax rates over time, why does a single premium deferred contract (SPDA) provide greater after tax rates of return than does a money market account? How is the difference in after tax accumulations in these two vehicles affected by the level of interest rates? Why does the length of the holding period affect the after tax rates of return per period on SPDAs and not on money market accounts? Annuity
An annuity is a series of equal payment made at equal intervals during a period of time. In other words annuity is a contract between insurer and insurance company in which insurer make a lump-sum payment or a series of payment and, in return,...