Which of the following features are correct? Choose correct option. a. The respiratory rhythm centre is located in the medulla oblongata. b. A chemosensitive area is situated adjacent to the rhythm centre. c. The pneumotaxic centre in the pons can modify the functions of the respiratory rhythm centre. d. Receptors associated with aortic arch and carotid artery can recognise changes in CO₂ and H⁺ concentration.