Please Help!!! I'm thinking the answer is A.
The photograph shows a laboratory investigator examining samples of DNA in a procedure called PCR, or polymerase chain reaction. Using PCR, the investigator can create thousands or even millions of copies of a fragment of DNA for closer investigation. In which of these situations would PCR be most useful?
A. When only a small amount of DNA is available, such as at a crime scene
B. When the DNA of identical twins is being mapped
C. When the genome of a population is being analyzed for preventable diseases
D. When the blood type of a DNA donor is known