What is an equivalence partition (also known as an equivalence class.?

A. A set of test cases for testing classes of objects
B. An input or output range of values such that only one value in the range becomes a test case
C. An input or output range of values such that each value in the range becomes a test case
D. An input or output range of values such that every tenth value in the range becomes a test case.
Ans:  ‘B’