
If the absolute values of the net charge of the peptide at $pH =2, pH =6$, and $pH =11$ are $\left| z _1\right|,\left| z _2\right|$ and $\left|z_3\right|$, respectively, then what is $\left|z_1\right|+\left|z_2\right|+\left|z_3\right|$ ?
$(A)$ Glucose $(B)$ Gulose
$(C)$ Fructose $(D)$ Maltose
$(E)$ Mannose
$\mathop {\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{COOH\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{H - C - OH\,\,\,\,\,\,\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}} \\
{Br - C - H\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,\,\,COOC{H_3}}
\end{array}}\limits_{(I)} $ $\mathop {\begin{array}{*{20}{c}}
{\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,COOC{H_3}\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{H - C - Br\,\,\,\,\,\,\,\,\,\,\,} \\
{|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}
\end{array}} \\
{HO - C - H\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,\,|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\
{\,\,\,\,\,\,\,COOH\,\,\,\,\,\,\,\,}
\end{array}}\limits_{(II)} $