The correct answer is A) It is insensitive to small over current. The main drawback or deficiency with the use of fuses is that they are insensitive to small overcurrent conditions. Fuses are designed to protect against high-level short-circuit faults, but they may not reliably trip for smaller overload conditions that can still damage equipment over time. This makes fuses less suitable for providing comprehensive overcurrent protection, as they may not respond quickly enough to prevent damage from lower-level overloads. The other options are incorrect because fuses do provide protection against short-circuit faults, operate quickly at high fault currents, and do generate heat when activated, which is a normal part of their operation.