我国季风区与非季风区的划分界线是                       

A．大兴安岭——太行山——巫山——雪峰山

B．天山——阴山

C．昆仑山——秦岭

D．大兴安岭——阴山——贺兰山

Reportedly on April 15, 2013 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