A company plans to create a database based on the following information: A department has at least one employee and usually employs many employees. Each employee cannot work with more than one department. For some reasons, some employees are not assigned to any department. A project must have at least one employee assigned to it and may have many employees assigned to it. An employee may be assigned to many projects. However, some employees may not work on any project. Each department is managed by a manager who is also an employee, and a manager cannot manage more than one department. Each department is uniquely identified by a department name and has 1 to 3 phone numbers. Each employee is uniquely identified by an employee number and has a name which consists of last name and first name. Each project is uniquely identified by project number and has a start date, end date, and duration. Questions: (1) List the main entity types. (2) List the main relationship types between the entity types