---Three people got killed by two explosions.

---When was __________?

---________ was on April 15 __________ the 2013 Boston Marathon was being held．

A．that; It; when

B．this; This; that

C．this; It; when

D．that; It; that

预防儿童少年发生意外事故的主要措施是（）

A.远离危险地方

B.积极开展健康教育

C.家长看住自己的孩子

D.学校要管理好学生

E.学生自己管好自己