c
\(\begin{array}{l}
Let\,'t'\,be\,the\,\,time\,taken\,by\,the\,bullet\,\,to\,hit\,the\,{\rm{target}}{\rm{.}}\\
\therefore \,{\rm{700 = }}\,{\rm{m = 63}}{{\rm{0}}^{ - 1}}t\\
 \Rightarrow t = \frac{{700m}}{{630m{s^{ - 1}}}} = \frac{{10}}{9}\sec \\
For\,velrtical\,motion,\\
Here,\,u = 0\\
\therefore \,h = \frac{1}{2}g{t^2}
\end{array}\)

\(\begin{array}{l}
 = \frac{1}{2} \times 10 \times {\left( {\frac{{10}}{9}} \right)^2}\\
 = \frac{{500}}{{81}}m = 6.17\,m\\
Therefore,\,the\,rifle\,must\,be\,{\rm{aimed}}\,{\rm{6}}{\rm{.17}}\,{\rm{m}}\,{\rm{above}}\,{\rm{the}}\,{\rm{center}}\,{\rm{of}}\,{\rm{the}}\,\\
{\rm{target}}\,{\rm{to}}\,{\rm{hit}}\,{\rm{the}}\,{\rm{target}}{\rm{.}}\,
\end{array}\)