A question about conformance of instances to ER schemas. Assume an ER schema with entity types Reader and Book, and relationship type Borrow between Reader and Book. Reader has two attributes memberid and name, where memberid is the key. Book has two attributes ISBN, author, and title, where ISBN is the key. The edge from Borrow to Reader is functional. Borrow has one attribute date. Which of the following statements is correct?

In an instance conforming to this schema, it is allowed that some Book entities have values for author and title, but not for ISBN.

There are instances conforming to this schema where the same Book is involved in multiple relationships.

There are instances conforming to this schema where the same Reader is involved in multiple relationships.

There are instances conforming to this schema that have no Borrow relationships.

In an instance conforming to this schema, every Borrow relationship must have a value for the date attribute.

There are instances conforming to this schema that have no Reader entities.