87. An unmarried child of a contributor is deemed to be his dependent child if he:(a) is less than 18 years of age, or
(b) is 18 or more years of age but less than 25 years of age and is in full time attendance at an educational institution substantially without interruption since the latest of the following dates: his eighteenth birthday, the day of the death of the contributor or the day on which the contributor becomes disabled, or
(c) is 18 or more years of age and is disabled, having been disabled without interruption since the later of the said dates.