Succinic Acid (HO₂CCH₂CH₂CO₂H) Is an Intermediate in the Kreb's Cycle $\approx$

Succinic acid (HO₂CCH₂CH₂CO₂H) is an intermediate in the Kreb's cycle used to "burn" carbohydrates, proteins and lipids. The formula for succinic acid can be abbreviated as H₂Sc.
H₂Sc(aq) + H₂O(l) H₃O⁺(aq) + HSc^-(aq)   K_a1 = 6.9 x 10^-5
HSc^-(aq) + H₂O(l) H₃O⁺(aq) + Sc^2-(aq)   K_a2 = 2.5 x 10^-6
Which of the following assumptions may not be valid for solutions of succinic acid because the difference between K_a1 and K_a2 for H₂Sc is very small?

A) [H₃O⁺] $\approx$ K_w/[OH^-]
B) [H₂Sc] < [Sc^2-]
C) [HSc^- ] $\approx$ [H₃O⁺]
D) [H₂Sc] $\approx$ C_H2Sc
E) None of these assumptions are legitimate for this solution.