All of the following statements concerning Waiver of Premium riders are correct EXCEPT:
a) Once activated, the Waiver of Premium will continue until the insured's recovery or the maturity of the policy whatever occurs first
b) An insured who has recovered from a disabling injury will be required to repay the insurer for any premiums that were waived
c) Waiver of Premium riders require that disablement needs to last for a certain period of time
d) There is a maximum age limit for the Waiver of Premium rider to activate.