challenge: What two genes have been used to characterize Candidatus Accumulibacter phosphatis (CAP) populations at a higher resolution than 16S rRNA?
  
  A. Polyphosphate kinase (ppk1) and PHA synthase (phaA)
  B. Polyphosphate kinase (ppk2) and PHA synthase (phaC)
  C. Polyphosphate kinase (ppk1) and PHA synthase (phaC)
  D. Polyphosphate kinase (ppk1) and PHA synthase (phaD)
  Answer: 