9. _______________ Horses were injected with toxins of diseases until their blood built upimmunities. Then an antitoxin or serum was made from their blood. Serums to fight bothdiphtheria (白喉) and tetanus(破傷風)were developed in this way.
(A) Worldwide, the horse plays a role within human cultures and has done so for thousands of years.
(B) People of all ages with physical and mental disabilities obtain beneficial results from associationwith the horse.
(C) The horse has played a little-known but very important role in the field of medicine.
(D) Horse blood was once used as food by some nomadic tribes, who found it a convenientsource of nutrition when traveling.¯