The correct answer is B. Geometrical increase method.
A young and rapidly increasing city is likely to experience a high rate of population growth. This means that the population is likely to increase at an exponential rate, rather than a linear rate. The geometrical increase method is the most appropriate method for forecasting population in this situation.
The arithmetical increase method is a simple method that assumes that the population will increase at a constant rate. This is not a realistic assumption for a young and rapidly increasing city, as the population is likely to increase at an accelerating rate.
The incremental increase method is a more complex method that takes into account the fact that the population is likely to increase at an accelerating rate. However, it is still not as accurate as the geometrical increase method.
The graphical method is a visual method that can be used to forecast population. However, it is not as accurate as the other methods.
In conclusion, the geometrical increase method is the most appropriate method for forecasting population for a young and rapidly increasing city.