A divorced spouse annuity ends with the earliest of the last day of the month before the month in which the--
(a) Divorced spouse dies;
(b) Employee's entitlement to an annuity ends;
(c) Divorced spouse marries;
(d) Employee dies; or
(e) Divorced spouse becomes entitled to a retirement or disability insurance benefit under the Social Security Act based on a primary insurance amount which equals or exceeds the amount of the full divorced spouse annuity before reduction for age.