Indicate which property is illustrated in Step 2.

Step 1 12x + 2 + 5x + 1 = (12x + 2) + (5x + 1)
Step 2 = 12x + (2 + 5x) + 1
Step 3 = 12x + (5x + 2) + 1
Step 4 = (12x + 5x) + (2 + 1)
Step 5 = (12 + 5)x + (2 + 1)
Step 6 = 17x + 3

A.
distributive
B.
associative
C.
arithmetic fact
D.
commutative