Luria and Delbruck Grew Many Liquid Cultures of Bacteria Then

Luria and Delbruck grew many liquid cultures of bacteria then spread a small sample of each culture on nutrient agar infused with bacteriophage in separate petri plates. They assayed the number of bacterial colonies that formed on each plate.
-What did the results of the Luria Delbruck fluctuation experiment indicate?

A) All bacteria are naturally resistant to infection by phage.
B) Some individuals in any bacterial population are resistant to infection by phage.
C) Exposure to phage induces some bacteria to mutate and become resistant to phage.
D) Resistance to phage in bacteria is caused by random spontaneous mutation.
E) Some phage mutated to produce large plaques with sharp edges.