Which expression can you simplify by combining like terms?


CLEAR CHECK

6d2+5cd−3dc+86d2+5cd-3dc+8

12c2−8d2c+3dc+412c2-8d2c+3dc+4

7d2−3c2+6d−c7d2-3c2+6d-c

16c2+8cd+7c−8d