This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Who discovered polymerase chain reaction 
Select and explain. 
A. Walter Gilbert, B. Barbara Mcclintock, C. Frederick Sanger, D. Karry B mullis
D: Karry B mullis
Answer: D: Karry B mullis 
Explanation: Karry B mullis discovered PCR.