The correct answer is: A. 20 A
Fuses are generally not used beyond 20 A because they are not able to provide adequate protection for higher currents. Fuses work by melting when a current that is too high flows through them. This prevents the current from damaging the circuit or the equipment that is connected to it. However, fuses are only able to handle a certain amount of current before they melt. If the current is too high, the fuse will melt and break the circuit, which can cause a power outage.
For this reason, fuses are not used beyond 20 A. If a circuit requires a higher current, a circuit breaker is used instead. Circuit breakers are similar to fuses in that they work by interrupting the flow of current when it becomes too high. However, circuit breakers are able to handle higher currents than fuses, and they can be reset after they have been tripped. This makes them a more reliable way to protect circuits and equipment from damage.
The other options are incorrect because they are higher than the maximum current that a fuse can handle.