Enhancers and promoters are ______. In contrast, the heterodimer "TFIIA and TFIIB" are examples of __________.

a. trans-acting elements, cis-acting factors

b. cis-acting elements, trans-acting factors

c. cis-activating factors, trans-acting elements

d. trans-activating factors, cis-acting elements

I believe the answer is "d" but don't have anything to back it up. Please help.