<s>[INST] context: oxygen concentrator They are also known as pressure swing adsorbers. They can be considered as an alternative to a traditional supply where no reliable liquid oxygen supply is available, such as an off-shore site or a site where the safety criteria for liquid installations cannot be met. These devices can be small, designed to supply oxygen to a single patient or they can be large enough to supply oxygen for a medical gas pipeline system. The components of this system are: Duplex compressors and molecular sieves, receivers, dryers, vacuum pumps, filters, line pressure regulators, control system, oxygen performance monitoring system and back up cylinder manifold. Oxygen concentrators operate on the principle of adsorbing (under pressure) other gases in the atmosphere onto the surface of an adsorbent material, known as zeolite. Because oxygen is not adsorbed by the zeolite, it is free to pass through into the storage for use. Zeolite is hydrated aluminium silicates of the alkaline eah metals in a powder or granular form. The zeolite is sealed in a vessel known as sieve bed. The sieve beds operate in pairs, one adsorbs whilst the other regenerates. Ambient air is filtered and pressurised to about 137 kPa by a compressor and then exposed to a zeolite molecular sieve column, forming a very large surface area, at a ceain pressure. The sieve selectively retains nitrogen and other unwanted components of air. These are released into the atmosphere after heating the column and applying a vacuum. The changeover between the columns is made by a time switch. The process is capable of producing oxygen concentrations of about 95%. The remainder is made up of mainly argon with a small percentage of nitrogen. During closed circuit anaesthesia, argon accumulation could occur. Therefore, to avoid this, higher fresh gas flows are required. As the process generates a great deal of heat, hence ventilation and cooling are mandatory. If the plant fails, the emergency cylinder manifold will feed into the pipeline at higher concentrations (99.5%) than the plant's operating norm of 95%. This may have an effect on down line equipment, paicularly in the critical care areas. This low-flow (2-4 L/min), low-pressure system can provide continuous oxygen to the chronic obstructive pulmonary disease patients. A typical unit operates on mains supply and can provide up to 5 L/min of oxygen at a concentration of 94%. It can be piped around the home in small wall mounted outlets . [/INST] question: What is the concentration of oxygen supplied by oxygen concentrator:- | options: A: 90% and 96% B: 100% C: 30 and 60% D: 60% and 90% | answer: A </s>