Reportedly on April 15 three people including a Chinese girl were killed in the Bos

问题补充：

Reportedly on April 15, three people including a Chinese girl were killed in the Boston Marathon attacks when two bombs were , which shocked the whole world.

A. set about

B. set off

C. set up

D. set out

答案：

A. set about

(答案→)B. set off

C. set up

D. set out

解析：考查词组：A. set about出发B. set off引发，引爆C. set up建立D. set out出发，句意：据报道，4月15号，在波斯顿马拉松爆炸案中当炸弹引爆的时候，有三人包括一个中国女孩丧生，这件事震惊了全世界。选B。