\(A = {{ - 5} \over {11}} + \left( {{{ - 6} \over {11}} + 1} \right)\)

\(=\frac{-11}{11}+1=-1+1=0\)

\(B = {2 \over 3} + \left( {{5 \over 7} + {{ - 2} \over 3}} \right)\)

\(= {2 \over 3} +{5 \over 7} +{{ - 2} \over 3}\)

\(=\frac{2}{3}+\frac{-2}{3}+\frac{5}{7}=0+\frac{5}{7}=\frac{5}{7}\)

\(C = \left( {{{ - 1} \over 4} + {5 \over 8}} \right) + {{ - 3} \over 8}\)

\(={{ - 1} \over 4}+{5 \over 8}+ {{ - 3} \over 8}\)

\(=\frac{-1}{4}+\frac{2}{8}=\frac{-1}{4}+\frac{1}{4}=0\)