( A ) A chemosensitive area is situated adjacent to the rhythm centre (in medulla) which is highly sensitive to CO2 and hydrogen ions.
( B ) Increase in CO2 and hydrogen ions can activate this centre, which in turn can signal the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated.
( C ) none of the above
( D ) Receptors associated with aortic arch and carotid artery also can recognise changes in CO2 and H+ concentration and send necessary signals to the rhythm centre for remedial actions
