问题补充:
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
答案:
A. to leave untreating
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.