Which expression is equivalent to 6^4 x 6^3?
A. (6x6x6x6)+(6x6x6)
B. (6+6+6+6) x (6+6+6)
C. (6x6x6x6) x (6x6x6)
D. (6x6x6x6x6) x (6x6x6x6)