People in Nome all had diphtheria a disease that spreads very fast. If it would produce

问题补充：

People in Nome all had diphtheria, a disease that spreads very fast. If , it would produce a powerful poison that would kill the patient.

A. untreating

B. to untreat

C. untreated

D. untreat

答案：

A. untreating

B. to untreat

(答案→)C. untreated

D. untreat

解析：这题考查if条件句的省略，如果主从句的主语一致，可以省略从句的主语和be动词，这句话的if条件句是省略的，所以是主语a disease被省略了，a disease和untreat之间是被动关系，所以用C。