The Following Question Refers to the Figure

Multiple Choice

The following question refers to the figure.
In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.

The cells in the 12 cell lines grown in low-glucose conditions showed the effects of which of the following processes?

A) gene flow and genetic drift
B) natural selection and mutation
C) natural selection and gene flow
D) conjugation and transformation