Subtraction is not commutative. For example, 3−2 = 2−3 since 3−2=1 and 2−3=−1. The equation x−y=y−x must then be false.

Division is also not commutative. For example, 4÷2 = 2÷4 since 4÷2=2 and 2÷4=1. The second equation m÷p=p÷mm÷p=p÷m must then be false.

Subtraction is also not associative. Distributing the negative on the right side of the equation (d−e)−f=d−(e−f) gives (d−e)−f=d−e+f. The two sides are then not equal since the left side has −f and the right side has ff. The third equation is then false.

Addition is associative. The Associative Property of Addition states that (a+b)+c=a+(b+c). Therefore (r+s)+t=r+(s+t). The correct answer is then choice D.

Division is also not commutative. For example, 4÷2 = 2÷4 since 4÷2=2 and 2÷4=1. The second equation m÷p=p÷mm÷p=p÷m must then be false.

Subtraction is also not associative. Distributing the negative on the right side of the equation (d−e)−f=d−(e−f) gives (d−e)−f=d−e+f. The two sides are then not equal since the left side has −f and the right side has ff. The third equation is then false.

Addition is associative. The Associative Property of Addition states that (a+b)+c=a+(b+c). Therefore (r+s)+t=r+(s+t). The correct answer is then choice D.