A solution contains compound X, which is a weak base, and its conjugate acid, in a molar ratio of 1:3. The resulting solution has pH 10.46. Based on the Kb values below, which is compound X?

A. (CH₃)₂NH Kb=5.9 x 10⁻⁴
B. NH₃Kb=1.8 x 10⁻⁵
C. C₆H₅NH₂Kb=4.0 x 10⁻¹⁰
D. (CH₃CH₂)₂NH Kb=8.7 x 10⁻⁴