Number three, we need heat resistant DNA polymerase. So the reason we need a heat resistant one is because we're going to carry out the reaction at a relatively high temperature. Now, a DNA polymerase is needed because that's the protein complex that moves along that DNA and replicates that DNA. And number four, we actually need the four different types of deoxyribonucleocide triphosphate. So remember, we have adenine, guanine, we also have cytosine and thymine. We need these four ingredients to actually produce that sequence of DNA that we want to amplify.