If an individual in receipt of an annuity renders compensated service, he shall not be paid an annuity with respect to any month in which such service is rendered to:

(a) An employer;

(b) Any person whether or not an employer by whom he was most recently employed when his annuity begins to accrue;

(c) Any person with whom he held, at the time the annuity begins to accrue, any rights to return to service;

(d) Any person with whom he ceased service in order to have his annuity begin to accrue.