Ans: C
Let $\sigma$ be the standard deviation of the examination.
$\begin{array}{rcl}
\dfrac{25-45}{\sigma} & = & -5 \\
\sigma & = & 4
\end{array}$
Let $x$ be the examination score of the girl.
$\begin{array}{rcl}
\dfrac{x-45}{4} & = & 7 \\
x & = & 73
\end{array}$
