Which of the following is one role of rna polymerase during transcription?
to switch uracil with thymine on the exposed gene
to build a molecule of mrna
to break down an already existing protein
to produce a start sequence

Lso known as DNA-dependent RNA polymerase, is an enzyme that produces primary transcript RNA. In cells, RNAP is necessary for constructing RNA chains using DNA genes as templates, a process called transcription. RNA polymerase enzymes are essential to life and are found in all organisms and many viruses. In chemical terms, RNAP is a nucleotidyl transferase that polymerizes ribonucleotides at the 3' end of an RNA transcript.
so the answer is to build a molecule of mRNA