SARS is an illness that can result in death unless left in time.A. to treatB. treatingC. t

问题补充：

SARS is an illness that can result in death unless left in time.

A. to treat

B. treating

C. treated

D. treat

答案：

A. to treat

B. treating

(答案→)C. treated

D. treat

解析：本句中的treat 充当主语补足语，且与主语SARS之间为被动关系，故应选择过去分词。