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