问题补充：
Spelling Bee is a contest competitors, usually children, are asked to spell as many words as possible.
A. which
B. where
C. what
D. When
答案：
A. which
(答案→)B. where
C. what
D. When
解析：考查从句，从句competitors, usually children, are asked to spell as many words as possible.不缺少成份，所以在关系副词里选择引导词，所以选B
