An expert system is a computer system that has specific knowledge in a professional field and can solve problems or give suggestions in this field. It is a more successful example in the field of artificial intelligence. According to the above definition, which of the following is expert systems? ['Online banking system. Through this system, users can manage their accounts online.', 'Office automation system. With electronic repeaters as the center, the word processor, fax machine, printer and other office equipment are organically combined for daily office use.', 'Dark Blue System. A computer system specially developed by IBM for chess competitions.', 'Bus query system. Through this system, users can query the stops of various buses.']