Dna is composed of two strands?

dna is composed of two strands, only one of which typically is used as a template for rna synthesis. By what mechanism is the correct strand chosen? A-Both strands are tried and the one that works is remembered, B-Only one strand has the start codon, c-the promoter acts to aim the rna polymerase, d-a start factor informs the system, e-it is chosen randomly.