Ans: B
The area in the map $:$ the actual area
The area in the map $:$ the actual area
$\begin{array}{cl}
= & 300 \text{ cm}^2 : 0.75 \text{ km}^2 \\
= & 300 \text{ cm}^2 : 0.75 \times 100000 \times 100000 \text{ cm}^2 \\
= & 300 : 7\ 500\ 000\ 000 \\
= & 1 : 25\ 000\ 000
\end{array}$
Therefore, the length in the map $:$ the actual length
$\begin{array}{cl}
= & \sqrt{1} : \sqrt{25\ 000\ 000} \\
= & 1 : 5\ 000
\end{array}$
Hence, the scale of the map is $1:5000$.
