a. 4 – commutative property
b. 5 – commutative property
c. 0 – identity property
d. 4 – associative property
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The commutative property lets you swap the order: (a) + (b) = (b) + (a).
The associative property lets you change the grouping: (a+b)+c = a+(b+c).
The identity property lets you add 0 without changing anything: (a) +0 = (a).