问题补充：
The doctors did all theythe sick man back to life.
A. could bring
B. could to bring
C. could bringing
D. cuold to bringing
答案：
A. could bring
(答案→)B. could to bring
C. could bringing
D. cuold to bringing
解析：这句话的意思是“医生们做他们能够做的一切来挽救这个病人的生命”。do all they can(do)to do…可以理解为定语从句，其先行词是all，关系代词that被省掉。此外还可以表达为do everything(that)they can(do)to do…或do what they can(do)to do…。
