Chloroacetic acid (pKa $2.86$) is more acidic than acetic acid (pKa $4.76$). Assume that the lowering of pKa produced by a chlorine atom is the full alpha effect when Cl is on the alpha carbon (C-2), and that it falls by a factor of $0.4$ for each additional carbon the chlorine moves away from the alpha carbon (beta-chloro, C-3: factor $0.4$; gamma-chloro, C-4: factor $0.4^2$). Butanoic acid has pKa $4.82$. The estimated pKa of 4-chlorobutanoic acid is

1. A$2.92$
2. B$4.52$
3. C$4.35$
4. D$4.06$