Which expressions are completely factored?

Select each correct answer.

A. 16a^5−20a^3=4^3(4a^2−5)

B. 24a^4+18=6(4a^4+3)

C. 30a^6−24a^2=3a^2(10a^4−8)

D. 12a^3+8a=4(3a^3+2a)