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

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

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

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.

1. A.
   while
2. B.
   where
3. C.
   when
4. D.
   then

 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