Final answer:
It is true that longer time periods are used to calculate indirect-cost rates to account for seasonal fluctuations, providing a more accurate reflection of costs over an entire year.
Step-by-step explanation:
True: One reason for using longer time periods to calculate indirect-cost rates is to account for seasonal cost fluctuations. By spreading costs over longer periods, businesses can attain a more accurate reflection of indirect costs throughout the entire year, mitigating the distortions arising from highs and lows that can occur in shorter time spans due to seasonality. This is particularly important for smaller economies where capital and goods movements might cause more volatile inflation.