问题
选择题
Up to Tuesday's attack, the worst school shooting in the U. S. was in March 1998 in Jonesboro,________ two boys, aged 11 and 13, shot and killed a teacher and four girls.
A．while
B．where
C．when
D．then
答案
答案：C
本题关键是辨明横线后为完整句“two boys，aged 11 and 13，shot and killed a teacher and four girls'’，其中aged 11 and 13为插入语。