For each of the following descriptions, draw an ER diagram showing entities, attributes, and relationships and their multiplicities. Where necessary, state any assumptions.

1. Customers are identified by a name and have an address. They purchase items. Items are identified by a number and have a colour. The quantity bought of each item is recorded.
2. Students are allowed to register in only one program at any given time. They enrol in courses in each semester. Students can enrol in the same course multiple times across different semesters. The system keeps track of marks obtained in each enrolment.
3. A real estate agency keeps track of rental properties their agents manage. Each property has a unique address and other attributes, such as no. of bedrooms, no. of car spaces and type (unit |house| semi-detached). Each property is owned by one or more landlords. Landlords are uniquely identified by their email address. Each property is assigned to an agent. At any given point in time, there can be only one active rental contract but, it is required to retain all expired contracts as well. There could be one or more tenants party to a contract. A contract has a unique contract number, monthly rental, bond amount and start and end dates.