The Following Structure Has Been Used in Monitoring the Development $\textbf{ 2011, }$

The following structure has been used in monitoring the development of amyloid plaques in Alzheimer's patients (J. Med. Chem. $\textbf{ 2011, }$ 949) . Which sequence correctly ranks the following nitrogens in order of increasing pK_b value?

A) 2 < 3 < 1
B) 3 < 2 < 1
C) 2 < 1 < 3
D) 1 < 3 < 2