What Is the Polymerase Chain Reaction (PCR)

What is the polymerase chain reaction (PCR) ?

A) PCR selects variations of genes within DNA,called alleles,to increase the fitness of organisms by artificial selection.
B) PCR produces many copies of a DNA sequence from a small sample using temperature cycling,primers,free nucleotides,and polymerase enzymes.
C) PCR modifies DNA within organisms,often species of agricultural importance,to increase the occurrence of desirable traits.
D) PCR determines the base pairs in a DNA sequence using temperature cycling,primers,fluorescent dye labels,and polymerase enzymes.
E) PCR amplifies DNA within an organism to increase the expression of that DNA for the purpose of studying its effects.