Which of the following statements regarding the bicarbonate-carbonic acid buffer system is correct? ...

Which of the following statements regarding the bicarbonate-carbonic acid buffer system is correct?
 
  A. The lungs regulate the carbonic acid concentration of the blood by regulating alveolar PCO2.
  B. The kidneys regulate the carbonic acid concentration of the blood by forming carbonic acid within the tubular epithelial cells.
  C. The kidneys regulate the bicarbonate concentration of the blood by secreting bicarbonate ions into the tubular filtrate.
  D. A fall in the bicarbonate concentration of the blood resulting from buffering (neutralizing) acid ketone bodies in a person with diabetic ketoacidosis is associated with a corresponding rise in blood PCO2 and carbonic acid.