Consider the following statements regarding regulation of respiration. a. Role of oxygen is insignificant in regulation of respiratory rhythm. b. An increase in concentration of CO2 and H+ ions, in arterial blood, activate chemosensitive area, which in turn signals pneumotaxic centre to make necessary adjustments. c. Respiratory rhythm centre in medulla is primarily responsible for regulation of respiration. d. Neural signals from pneumotaxic centre can increase the duration of inspiration. Choose the option that mentions all correct statements.