This is an illness that can result in total blindness if .
A. to leave untreating
B. left untreated
C. leaving untreating
D. is left untreated
网友回答
A. to leave untreating
(答案→)B. left untreated
C. leaving untreating
D. is left untreated
解析：状语从句的省略形式，其完整形式是： ... if it is left untreated.