The correct answer is: C. Vacuum circuit breakers
Vacuum circuit breakers have high reliability and minimum maintenance because they do not have any moving parts. They are also very fast, making them ideal for use in high-voltage applications.
Air blast circuit breakers use compressed air to extinguish the arc. They are reliable and have a long life, but they require regular maintenance to ensure that the air pressure is correct.
Circuit breakers with SF6 gas use sulfur hexafluoride gas to extinguish the arc. SF6 is a very effective arc-extinguishing agent, and it is also non-toxic and non-flammable. However, SF6 is a greenhouse gas, and its use is being phased out in some countries.
Oil circuit breakers use oil to extinguish the arc. They are very reliable, but they are also heavy and require regular maintenance to ensure that the oil is clean and free of contaminants.
In conclusion, vacuum circuit breakers are the best option for applications that require high reliability and minimum maintenance.