Which indicator would be the most appropriate for titrating aqueous ethylamine, ${\text{C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{H}}_{\text{2}}}{\text{N}}{{\text{H}}_{\text{2}}}$, with nitric acid, ${\text{HN}}{{\text{O}}_{\text{3}}}$?

A.     Bromophenol blue ${\text{(p}}{K_{\text{a}}} = {\text{ }}4{\text{.}}1)$

B.     Bromothymol blue ${\text{(p}}{K_{\text{a}}} = {\text{ }}7{\text{.}}3)$

C.     Phenol red ${\text{(p}}{K_{\text{a}}} = {\text{ }}8{\text{.}}0)$

D.     Thymolphthalein ${\text{(p}}{K_{\text{a}}} = {\text{ }}10{\text{.}}0)$

A