This is an illness that can result in total blindness if ( ) untreated in time.A.being left B.left C.to be left D.leaving 英语
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【答案】 B left 表被动
if从句后省略了主语和be动词
即这句话完整为：This is an illness that can result in total blindness if (it is left ) untreated in time.
这个疾病如果不被及时治疗将会导致完全失明.