The length of the projection period is determined by the purpose of the projection and the time horizon of the underlying assumptions.
In general, the projection period is determined based on the time horizon of the underlying assumptions. For example, if the assumptions are based on a five-year plan, then the projection period may be set to five years.
However, the projection period may also be determined by the purpose of the projection. For example, if the projection is being used to determine the viability of a long-term investment, then the projection period may be longer than five years.
Therefore, the correct answer to this question is not provided in the options.