The Following Question Refers to the Figure

Multiple Choice

The following question refers to the figure.
In this eight-year experiment, a population of E. coli, begun from a single cell, was 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 population, and its ability to grow in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.
If the experimental population of E. coli lacks an F factor or F plasmid, and if bacteriophages are excluded from the bacterial cultures, how would beneficial mutations be transmitted horizontally to other E. coli cells?

A) sex pili
B) transduction
C) conjugation
D) transformation