问题补充：
The rescuers to work as soon as they arrived at the spot of the accident.
A. set out
B. set off
C. set up
D. set in
答案：
(答案→)A. set out
B. set off
C. set up
D. set in
解析：句意：救援人员一到出事地点，就开始工作了。使用：Set out to do sth.开始着手做…, B. set off成分，引发，引爆， C. set up建立，D. set in嵌入，所以选A。
