Final answer:
All options (BOOK, Book, Boo01k, book) represent valid equivalence classes for a text box accepting alphanumeric values, as they all contain alphanumeric characters.
Step-by-step explanation:
The term Valid Equivalence Class signifies a subset of data that is representative of a larger group, where all members of this subset behave in the same way for the testing purpose. When identifying a Valid Equivalence Class for a field on a form that accepts alphanumeric values, all options (A, B, C, D) represent valid equivalence classes because they all contain alphanumeric characters which the text box is designed to accept.
However, without specific instructions indicating a preference for case sensitivity or the inclusion of numeric characters, each choice (BOOK, Book, Boo01k, book) is equally valid as they all follow the general criterion of being alphanumeric.