With constant tax rates over time, why does a single$-$premium deferred annuity contract $($SPDA$)$ pro$-$ vide 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?