It basically means the building blocks, the ribonucleotide triphosphates and there are four different types. So we have adenosine five triphosphate we have guanosine five triphosphate we have citadine five prime triphosphate and we have uridine five prime triphosphate. And these building blocks are needed to actually synthesize and elongate that polynucleotide chain. Now, number two, it actually needs a preexisting DNA template molecule. So usually we're dealing with a double stranded DNA molecule and a double stranded DNA molecule works the best. But in some cases we can also use single stranded DNA molecules as templates.