During the Long-Term Evolution Experiment (LTEE), investigators found a Cit⁺ strain of Escherichia coli that allowed fast growth on citrate buffer after 33,000 generations. The ability to catabolize citrate evolved at this time through

A) acquiring the ability to exploit new ecological niches.
B) becoming pathogens.
C) becoming dependant on a symbiotic partner's resources.
D) becoming pathogens and becoming dependent on a symbiotic partner's resources.
E) losing the ability to exploit new ecological niches.