Imagine two closely related species. In species A, brood care is limited to the offspring's ...

Imagine two closely related species. In species A, brood care is limited to the offspring's parents. In species B, parents do not contribute to brood care at all; the same amount of brood care as in species A is instead pro-vided by grandparents.
 
  Each generation produces only one litter of offspring. In both cases, brood care is crucial to the survival of the offspring. Which species may see the earlier onset of senescence, provided that all other factors such as ex-trinsic mortality are equal?
  a. Species A, as parents are exposed to both the rigors of reproduction and brood care in quick succession.
  b. Species A, as a mutation later in life will impact inclusive fitness less than it would impact in-clusive fitness in species B.
  c. There would be no difference, as the smaller relatedness of grandparents to their offspring would diminish any fitness advantages of grandparental brood care.
  d. There would be no difference, as the selection against mutations later in life would be counter-balanced by more tolerance for mutations early in life.