What are the complementary bases that RNA polymerase adds during elongation?

During the elongation phase of transcription, RNA polymerase synthesizes RNA by adding ribonucleotides that are complementary to the DNA template strand. The base pairing rules for RNA differ slightly from those of DNA due to the inclusion of uracil (U) in RNA instead of thymine (T).

In RNA pairing, adenine (A) from the DNA template pairs with uracil (U) in the RNA, and cytosine (C) from the DNA pairs with guanine (G) in the RNA. This means that the pairs formed are A-U and G-C during the synthesis process.

Thus, the bases added by RNA polymerase that are complementary to the bases in the DNA template are indeed A-U and G-C, making this the correct choice. Understanding these base pairings is fundamental to grasping how genetic information is transcribed into RNA, which subsequently leads to translation into proteins.