What is a matrix?

A matrix is a rectangular array of real numbers arranged in rows and columns.
The order of a matrix is given by the indicated product m x n, where 'm' indicates the number of rows and 'n' the number of columns.
A matrix is denoted by uppercase letters, such as A, B, C, D, etc.
A matrix is always a square array of numbers.
a) I and II are correct.
b) II and III are correct.
c) I, II, and III are correct.
d) II, III, and IV are correct.