A digital school library system stores a book's title author and availability. On what basis does availability information change?

Correct answer: On issue and return transactions

The governing concept is that a digital record represents a real-world event or transaction. When the book is issued, its status changes from available to issued; when it is returned, the status can change back to available. Thus option B is correct. The cover colour, wall colour, and student height do not cause a library transaction or logically determine the availability field.