simplify the sum: (5u^3+7u^2+7)+(7u^3-6u+5)

A) 12u^3+7u^2-6u+12
B) -2u^3+7u^2-6u+12
C) 12u^3+6u^2-7u+12
D) -2u^3-6u^2+7u-12