Do \(\dfrac{10^{18}+1}{10^{19}+2}< 1\Rightarrow B< \dfrac{10^{18}+1+9}{10^{19}+1+9}\)
\(\Rightarrow B< \dfrac{10^{18}+10}{10^{19}+10}\)
\(\Rightarrow B< \dfrac{10\left(10^{17}+1\right)}{10\left(10^{18}+1\right)}\)
\(\Rightarrow B< \dfrac{10^{17}+1}{10^{18}+1}\)
\(\Rightarrow B< A\)