Which of the following correctly demonstrates the Associative Property of Addition? (1 m(xy) = (mx) * y; x(y + z) = (xy) + z; (x + y) + z + r = x + (y + z) + r; y - (x + 1) = (y - x) + 1

The correct demonstration of the Associative Property of Addition from your list is:

\((x + y) + z + r = x + (y + z) + r\).

The Associative Property of Addition states that the grouping of numbers does not affect their sum. In other words, when you are adding three or more numbers, you can add them in any grouping without changing the result.