ChinaTravel Agents (CTA) wants a database to keep information about its many offices and the people involved in its operations, and about airline companies and the flights they offer. Every office has a unique number and an address. For each person, we need to store the name, the address, one home phone number, and a unique ID number. If the person is an CTA employee we also need to store his/her EID and business phone number, as well as the office he/she works for. Some CTA employees are managers. For each manager it is required to know their qualifications, their annual salary, and the set of offices under their management. Note that, for agents (=CTA employees who are not managers), we store their hourly pay rate. A person can book a flight via an agent (who is not a manager). For each flight we need the following information: flight number, airport code, date of departure, and destination. Flight numbers are unique only within the same airline. When a flight is booked we need to know the date of booking and the price. Each airline company offers a set of flights, and has a unique code, a name, and a list of phone numbers with a description for each phone number. Design an (Enhanced) Entity Relationship diagram according to the above requirements. Make sure to indicate constraints.