Notwithstanding paragraph (2) of this subsection, compensation payable to or for a child, a brother or sister, or grandchild that would otherwise end because the child, brother or sister, or grandchild has reached 18 years of age shall continue if he is a student as defined by section
8101 of this title at the time he reaches 18 years of age for so long as he continues to be such a student or until he marries. A widow or widower who has entitlements to benefits under this title derived from more than one husband or wife shall elect one entitlement to be utilized.