The earth - quake took place on      Friday afternoon in March and did     great damage to the country.

A．/; /

B．a; a

C．a; /

D．the; a

破伤风杆菌的致病因素是()
志贺痢疾杆菌的致病因素是()
伤寒杆菌的致病因素是()
结核杆菌的致病因素是()

A．外毒素

B．内霉素

C．两者均有

D．两者均无