Explanation: The deviation ratio for an FM signal is a fundamental parameter that describes the relationship between the maximum frequency deviation and the maximum modulation frequency (highest audio frequency) accepted by the system. It's crucial for understanding the bandwidth requirements of an FM transmission. The formula for deviation ratio (DR) is: DR = Maximum Frequency Deviation / Maximum Modulation Frequency Given values: Maximum Frequency Deviation ($\Delta f$) = 5 kHz Maximum Modulation Rate ($f_m$) = 3 kHz Plugging these values into the formula: DR = 5 kHz / 3 kHz = 1.666... Rounding to two decimal places, the deviation ratio is 1.67, which corresponds to option D) 1.66. Options A, B, and C are incorrect. Option C (0.6) would result from inverting the formula, dividing the maximum modulation frequency by the maximum frequency deviation (3 kHz / 5 kHz), which is not the correct definition of deviation ratio.