Which expression represents the second partial sum for [blank]?
a) (S₂ = n/2(2a₁ + (n-1)d))
b) (S₂ = n/2(a₁ + a₂))
c) (S₂ = n/2(a₁ + aₙ))
d) (S₂ = n/2(2a₁ + (n-1)d))